feat(07-02): add QuickAdd API client, hook, management page, routing, and i18n

- Added QuickAddItem interface and quickAdd namespace to api.ts
- Created useQuickAdd hook with CRUD operations following useTemplate pattern
- Created QuickAddPage with amber/orange gradient header, add form, inline edit, and EmptyState
- Added /quick-add route to App.tsx with QuickAddPage import
- Added Zap nav item to AppLayout sidebar after template
- Added quickAdd i18n keys to en.json and de.json including picker keys

frontend/src/App.tsx

@@ -8,6 +8,7 @@ import { DashboardPage } from '@/pages/DashboardPage'
 import { CategoriesPage } from '@/pages/CategoriesPage'
 import { SettingsPage } from '@/pages/SettingsPage'
 import { TemplatePage } from '@/pages/TemplatePage'
+import { QuickAddPage } from '@/pages/QuickAddPage'
 import '@/i18n'
 
 export default function App() {
@@ -37,6 +38,7 @@ export default function App() {
           <Route path="/" element={<DashboardPage />} />
           <Route path="/categories" element={<CategoriesPage />} />
           <Route path="/template" element={<TemplatePage />} />
+          <Route path="/quick-add" element={<QuickAddPage />} />
           <Route path="/settings" element={<SettingsPage user={auth.user} onUpdate={auth.refetch} />} />
         </Routes>
       </AppLayout>