feat: draft mode, admin branding, and workflow improvements

Draft Mode:
- Events are created as drafts by default — no email sent until published
- Add "Publish & Notify Client" button with confirmation dialog
- Draft banner with yellow styling on event details page
- Draft filter tab in events list
- Gallery middleware blocks public access to draft events
- Migration 076 adds is_draft column to events table

Admin Draft Preview:
- Admins can preview draft galleries via JWT preview token (?preview=)
- "View Gallery" link on drafts auto-appends preview token

Admin & Login Page Branding:
- Admin header uses configured company logo/name from branding settings
- Login page shows configured logo instead of hardcoded PicPeak
- Respects logo_display_mode (logo_only, text_only, logo_and_text)

OG Tag Branding:
- DynamicFavicon component updates OG meta tags and page title from
  branding settings

Editable Client Email:
- Customer email is now editable after event creation in edit mode

Branding Inheritance:
- New events inherit hero logo settings (visibility, size, position)
  from global branding configuration

Share Link Full Domain URL:
- New getFrontendBaseUrl() utility with DB fallback to general_site_url
- Used in email processor and share link service

backend/migrations/core/076_add_is_draft_column.js

@@ -0,0 +1,21 @@
+/**
+ * Migration to add is_draft column to events table.
+ * Draft events are not visible to gallery visitors until published.
+ */
+exports.up = async function(knex) {
+  const hasColumn = await knex.schema.hasColumn('events', 'is_draft');
+  if (!hasColumn) {
+    await knex.schema.alterTable('events', (table) => {
+      table.boolean('is_draft').defaultTo(false);
+    });
+  }
+};
+
+exports.down = async function(knex) {
+  const hasColumn = await knex.schema.hasColumn('events', 'is_draft');
+  if (hasColumn) {
+    await knex.schema.alterTable('events', (table) => {
+      table.dropColumn('is_draft');
+    });
+  }
+};