Add shared ai-service container as AI provider intermediary

All feature containers now POST messages to ai-service (port 8010) instead
of calling AI providers directly. ai-service routes to LM Studio, Ollama,
or Anthropic based on /config/ai_service_config.json. doc-service AI
providers removed; replaced by httpx ai_client.py. Backend settings
restructured to /api/settings/ai. Frontend gets dedicated AIAdminSettingsPage
and AI Service card in AppsPage.

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

frontend/src/App.tsx

@@ -9,6 +9,7 @@ import AppsPage from "./pages/AppsPage";
 import AdminPage from "./pages/AdminPage";
 import DocumentsPage from "./pages/DocumentsPage";
 import DocumentAdminSettingsPage from "./pages/DocumentAdminSettingsPage";
+import AIAdminSettingsPage from "./pages/AIAdminSettingsPage";
 
 function PrivateRoute({ children }: { children: React.ReactNode }) {
   const { token } = useAuth();
@@ -39,6 +40,10 @@ export default function App() {
         path="/apps/documents/settings/admin"
         element={<AdminRoute><DocumentAdminSettingsPage /></AdminRoute>}
       />
+      <Route
+        path="/apps/ai/settings/admin"
+        element={<AdminRoute><AIAdminSettingsPage /></AdminRoute>}
+      />
       <Route path="/profile" element={<PrivateRoute><ProfilePage /></PrivateRoute>} />
       <Route path="/admin" element={<AdminRoute><AdminPage /></AdminRoute>} />