feat: unified ContentCreation tool (Object + Statement creation merged)

- New ContentCreation.jsx: 3-column layout
  Left: object list + "＋ Objekt hinzufügen" button
  Center: dual-mode canvas (draw OR highlight)
  Right: ObjectAddPanel (mode=add) or PairsPanel (mode=objectId)
- After saving object → auto-switches to PairsPanel for that object
- All ObjectCreation + StatementCreation logic merged into one page
- All pictures loaded (no objects_created filter)
- "Objekte abgeschlossen" button marks picture (visual badge)
- ContentHub: 2 tiles (Content Erstellen + Veröffentlichen placeholder)
- App.jsx: /content/creation route, old /content/objects + /content/statements removed

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/App.jsx

@@ -5,8 +5,7 @@ import Dashboard from './pages/Dashboard';
 import DatabaseAdmin from './pages/DatabaseAdmin';
 import TableView from './pages/TableView';
 import ContentHub from './pages/ContentHub';
-import ObjectCreation from './pages/ObjectCreation';
-import StatementCreation from './pages/StatementCreation';
+import ContentCreation from './pages/ContentCreation';
 
 function RequireAuth({ children }) {
   const user = getUser();
@@ -23,8 +22,7 @@ export default function App() {
         <Route path="/db" element={<RequireAuth><DatabaseAdmin /></RequireAuth>} />
         <Route path="/db/:tableKey" element={<RequireAuth><TableView /></RequireAuth>} />
         <Route path="/content" element={<RequireAuth><ContentHub /></RequireAuth>} />
-        <Route path="/content/objects" element={<RequireAuth><ObjectCreation /></RequireAuth>} />
-        <Route path="/content/statements" element={<RequireAuth><StatementCreation /></RequireAuth>} />
+        <Route path="/content/creation" element={<RequireAuth><ContentCreation /></RequireAuth>} />
         <Route path="*" element={<Navigate to="/" replace />} />
       </Routes>
     </BrowserRouter>