feat(projects): Project Overview cockpit UI + CRM nav entry

- ProjectsListPage: searchable list + inline create, under CRM → Overview.
- ProjectCockpitPage: editable header, milestone timeline, and one dated
  feed merging emails (with sent-HTML preview modal + resend/cancel/retry/
  send-now actions), quotes, contracts, invoices, galleries and hours.
- Routes /admin/clients/projects(/:id) gated by RequireFeature flag=projects.
- ClientsLayout 'Overview' nav entry (top), gated on flags.projects.
- en + de i18n for the projects namespace + book-to-project label.

frontend/src/App.tsx

@@ -43,6 +43,8 @@ import { HoursLoggingPage } from './pages/admin/clients/HoursLoggingPage';
 const CalendarPage = lazy(() => import('./pages/admin/clients/CalendarPage').then((m) => ({ default: m.CalendarPage })));
 import { QuoteResponsePage } from './pages/public/QuoteResponsePage';
 import { ContractResponsePage } from './pages/public/ContractResponsePage';
+import { ProjectsListPage } from './pages/admin/projects/ProjectsListPage';
+import { ProjectCockpitPage } from './pages/admin/projects/ProjectCockpitPage';
 import { ContractsListPage } from './pages/admin/contracts/ContractsListPage';
 import { ContractEditorPage } from './pages/admin/contracts/ContractEditorPage';
 import { ContractDetailPage } from './pages/admin/contracts/ContractDetailPage';
@@ -202,6 +204,12 @@ function App() {
                             <Route path="quotes/:id" element={<QuoteDetailPage />} />
                             <Route path="quotes/:id/edit" element={<QuoteEditorPage />} />
                           </Route>
+                          {/* Project Overview (CRM) — admin-only grouping
+                              layer above events, gated by `projects`. */}
+                          <Route element={<RequireFeature flag="projects" />}>
+                            <Route path="projects" element={<ProjectsListPage />} />
+                            <Route path="projects/:id" element={<ProjectCockpitPage />} />
+                          </Route>
                           {/* Bills / invoices (CRM) — gated by `bills`. */}
                           <Route element={<RequireFeature flag="bills" />}>
                             <Route path="bills" element={<BillsListPage />} />