feat(settings): Features tab + sidebar reorg with feature-flag gating

Reorganises the admin sidebar around what users actually do, and adds a
single Features page that gates which feature surfaces appear in the
nav. Shrinks the main sidebar from 11 items to 4-6 (depending on
feature flags) and groups configuration screens into a single Settings
home with six logical sections.

Why
---
The current sidebar mixes three concerns: workspaces (Dashboard, Events,
Archives), feature surfaces (Analytics, Users), and configuration
screens that get touched maybe once a month (Email Settings, Branding,
Event Types, Backup, CMS Pages). That's 11 items, half of them config.

Backend
-------
- New `feature_flags` table (key, value, updated_at, updated_by).
  Migration 088 detects existing-vs-fresh installs from the events
  table:
    * Existing install (events>0)  → all 9 flags TRUE so nothing
      vanishes from an admin's UI on upgrade.
    * Fresh install      (events=0) → spec defaults: galleries,
      reminderEmails, analytics, userManagement TRUE; calendar,
      calendarBooking, quotes, bills, messaging FALSE.

- New `/api/admin/feature-flags` (GET/PUT) under `settings.view` and
  `settings.edit`. Server enforces the same dependency rules the
  frontend does (galleries always TRUE, quotes=false → bills=false,
  calendar=false → calendarBooking=false). PUT writes one
  `feature_flags_updated` activity log row with the diff.

Frontend
--------
- `FeatureFlagsContext` provides `useFeatureFlags()` (with staged/save/
  reset/isDirty) and `useFeatureEnabled(key)`. Mounted inside
  AdminLayout so flag fetches carry the auth cookie. Source of truth
  is the server response; staged is a local copy that the Features tab
  edits and the Save button PUTs.

- `RequireFeature` route guard for /admin/analytics and /admin/users —
  redirects to /admin/dashboard when the corresponding flag is OFF.

- AdminSidebar dropped from 11 to 6 items. Removed: Email Settings,
  Branding, Event Types, Backup, CMS Pages (now Settings tabs).
  Feature-gated: Analytics, Users.

- Old top-level routes (/admin/email, /admin/branding, /admin/event-
  types, /admin/backup, /admin/cms) kept as <Navigate> redirects to
  /admin/settings?tab=<key> so existing bookmarks don't 404.

- SettingsPage rewritten with a 6-group inner-nav (General /
  Content & Appearance / Communication / Privacy & Security /
  Integrations / System) and 19 tabs. New Features tab is the
  default landing tab. URL ?tab=<key> roundtrips with state — deep
  links and the back button work.

- FeaturesTab renders 9 cards across 5 sections. Toggles enabled for
  Analytics + User Management (the two flags that gate sidebar items
  in this PR). All other toggles disabled with a "Not yet available"
  lockedReason — the cards still render so admins see the roadmap, but
  the flag has no UI effect until the surface ships in its own PR. The
  galleries card is locked TRUE per spec (foundation, can't be off).

- Live SidebarPreview reflects unsaved staged changes — admins see
  what their sidebar will look like before they save.

- New i18n keys across all 5 locales (en, de, nl, pt, ru) for the
  Features tab copy, the new Settings group labels, and the lifted
  tab titles.

Verified end-to-end
-------------------
- Migration on this dev DB (existing install, 977 events): all 9 flags
  set to TRUE.
- Migration on simulated fresh install (events table emptied): spec
  defaults applied (5 OFF, 4 ON).
- Backend round-trip: GET → PUT → audit-log entry written, dependency
  rule enforced (bills forced false when quotes=false even when bills=
  true requested).
- UI Playwright spec: sidebar dropped 5 items, old top-level routes
  redirect, Features tab is default, Galleries+Calendar+Quotes+Bills+
  Messaging+ReminderEmails toggles disabled, Analytics+Users toggles
  enabled, toggling Analytics off + saving updates the sidebar +
  redirects /admin/analytics to /admin/dashboard.
- Smoke 13/13 still green; no regressions on existing flows.

frontend/src/components/admin/AdminLayout.tsx

@@ -2,6 +2,7 @@ import React, { useState } from 'react';
 import { Outlet, Navigate } from 'react-router-dom';
 
 import { useAdminAuth } from '../../contexts';
+import { FeatureFlagsProvider } from '../../contexts/FeatureFlagsContext';
 import { useSessionTimeout } from '../../hooks/useSessionTimeout';
 import { AdminSidebar } from './AdminSidebar';
 import { AdminHeader } from './AdminHeader';
@@ -30,6 +31,28 @@ export const AdminLayout: React.FC = () => {
     return <Navigate to="/admin/login" replace />;
   }
 
+  // FeatureFlagsProvider wraps the entire admin chrome — sidebar reads
+  // flags to decide which surfaces to render, the Features tab reads/writes
+  // the same source. Mounted INSIDE the auth-required tree so the GET to
+  // /api/admin/feature-flags has a session cookie attached.
+  return (
+    <FeatureFlagsProvider>
+      <AdminLayoutInner
+        sidebarOpen={sidebarOpen}
+        setSidebarOpen={setSidebarOpen}
+        mustChangePassword={mustChangePassword}
+      />
+    </FeatureFlagsProvider>
+  );
+};
+
+interface AdminLayoutInnerProps {
+  sidebarOpen: boolean;
+  setSidebarOpen: (v: boolean) => void;
+  mustChangePassword: boolean;
+}
+
+const AdminLayoutInner: React.FC<AdminLayoutInnerProps> = ({ sidebarOpen, setSidebarOpen, mustChangePassword }) => {
   return (
     <div className="h-screen bg-neutral-50 dark:bg-neutral-950 flex overflow-hidden">
       {/* Mandatory Password Change Modal */}

frontend/src/components/admin/AdminSidebar.tsx

@@ -3,51 +3,61 @@ import { NavLink, useLocation } from 'react-router-dom';
 import {
   LayoutDashboard,
   Calendar,
-  Mail,
   Archive,
   BarChart3,
   Settings,
   X,
-  Palette,
-  FileText,
-  HardDrive,
   Users,
-  Tags
 } from 'lucide-react';
 import { useQuery } from '@tanstack/react-query';
 import { useTranslation } from 'react-i18next';
 import { settingsService } from '../../services/settings.service';
 import { VersionInfo } from './VersionInfo';
 import { usePermissions } from '../../contexts/PermissionsContext';
+import { useFeatureFlags, type FeatureKey } from '../../contexts/FeatureFlagsContext';
 
 interface AdminSidebarProps {
   isOpen: boolean;
   onClose: () => void;
 }
 
-const navigation = [
+interface NavItem {
+  nameKey: string;
+  href: string;
+  icon: React.ComponentType<{ className?: string }>;
+  permission?: string | false;
+  featureFlag?: FeatureKey;
+}
+
+// Sidebar shape after the Settings reorg (#feature-flags-settings-reorg).
+//
+// Removed (now live as Settings tabs, with redirects from the old
+// top-level paths so bookmarks keep working):
+//   /admin/email, /admin/branding, /admin/event-types, /admin/backup,
+//   /admin/cms.
+//
+// Feature-gated (only render when the corresponding feature flag is on):
+//   Analytics → flags.analytics
+//   Users     → flags.userManagement
+const navigation: NavItem[] = [
   { nameKey: 'navigation.dashboard', href: '/admin/dashboard', icon: LayoutDashboard, permission: false },
-  { nameKey: 'navigation.events', href: '/admin/events', icon: Calendar, permission: 'events.view' },
-  { nameKey: 'navigation.archives', href: '/admin/archives', icon: Archive, permission: 'archives.view' },
-  { nameKey: 'admin.analytics', href: '/admin/analytics', icon: BarChart3, permission: 'analytics.view' },
-  { nameKey: 'navigation.emailSettings', href: '/admin/email', icon: Mail, permission: 'email.view' },
-  { nameKey: 'navigation.branding', href: '/admin/branding', icon: Palette, permission: 'branding.view' },
-  { nameKey: 'navigation.settings', href: '/admin/settings', icon: Settings, permission: 'settings.view' },
-  { nameKey: 'navigation.eventTypes', href: '/admin/event-types', icon: Tags, permission: 'settings.view' },
-  { nameKey: 'navigation.backup', href: '/admin/backup', icon: HardDrive, permission: 'backup.view' },
-  { nameKey: 'navigation.cmsPages', href: '/admin/cms', icon: FileText, permission: 'cms.view' },
-  { nameKey: 'navigation.users', href: '/admin/users', icon: Users, permission: 'users.view' },
-] as const;
+  { nameKey: 'navigation.events',    href: '/admin/events',    icon: Calendar,        permission: 'events.view' },
+  { nameKey: 'navigation.archives',  href: '/admin/archives',  icon: Archive,         permission: 'archives.view' },
+  { nameKey: 'admin.analytics',      href: '/admin/analytics', icon: BarChart3,       permission: 'analytics.view', featureFlag: 'analytics' },
+  { nameKey: 'navigation.settings',  href: '/admin/settings',  icon: Settings,        permission: 'settings.view' },
+  { nameKey: 'navigation.users',     href: '/admin/users',     icon: Users,           permission: 'users.view',     featureFlag: 'userManagement' },
+];
 
 export const AdminSidebar: React.FC<AdminSidebarProps> = ({ isOpen, onClose }) => {
   const location = useLocation();
   const { t } = useTranslation();
   const { hasPermission } = usePermissions();
+  const { flags } = useFeatureFlags();
 
-  // Filter navigation items based on permissions
-  const filteredNavigation = navigation.filter(item => {
-    if (!item.permission) return true;
-    return hasPermission(item.permission);
+  const filteredNavigation = navigation.filter((item) => {
+    if (item.permission && !hasPermission(item.permission as string)) return false;
+    if (item.featureFlag && !flags[item.featureFlag]) return false;
+    return true;
   });
 
   return (

frontend/src/components/admin/RequireFeature.tsx

@@ -0,0 +1,25 @@
+import React from 'react';
+import { Navigate, Outlet } from 'react-router-dom';
+import { useFeatureFlags, type FeatureKey } from '../../contexts/FeatureFlagsContext';
+
+interface RequireFeatureProps {
+  flag: FeatureKey;
+  fallback?: string;
+}
+
+/**
+ * Route guard that redirects to /admin/dashboard when the named feature
+ * flag is OFF. Used so deep links (or stale bookmarks) to disabled
+ * surfaces don't render an empty page or a half-loaded view.
+ *
+ * Mounted as the `element` of a parent <Route>, with the gated routes as
+ * children — see App.tsx.
+ */
+export const RequireFeature: React.FC<RequireFeatureProps> = ({ flag, fallback = '/admin/dashboard' }) => {
+  const { flags, isLoading } = useFeatureFlags();
+  // Wait for the first fetch — otherwise we'd briefly fall back to the
+  // default-flags object and could redirect on a transient false.
+  if (isLoading) return null;
+  if (!flags[flag]) return <Navigate to={fallback} replace />;
+  return <Outlet />;
+};