feat: add external links admin with drag-and-drop and e2e tests

This introduces a full CRUD interface for managing external link
sections and links, including drag-and-drop reordering across
sections using dnd-kit. Links can be toggled enabled/disabled and
are rendered on the start page grouped by section.

The server side adds Alembic migrations for the external_link_sections
and external_links tables, along with API routes for sections, links,
and bulk reorder operations. The debug endpoint now truncates these
tables between e2e test runs to ensure clean state.

E2e tests cover section and link creation, editing, deletion,
enable/disable toggling with start page verification, and multi-section
rendering on the start page.

Author: magkue

client/package-lock.json

@@ -13,6 +13,9 @@
     "format": "biome check src --write"
   },
   "dependencies": {
+    "@dnd-kit/core": "^6.3.1",
+    "@dnd-kit/sortable": "^10.0.0",
+    "@dnd-kit/utilities": "^3.2.2",
     "@hookform/resolvers": "^5.2.2",
     "@radix-ui/react-avatar": "^1.1.11",
     "@radix-ui/react-checkbox": "^1.3.3",

client/package.json

@@ -3,6 +3,7 @@ import { ProtectedRoute } from "@/components/layout/ProtectedRoute";
 import { AuthProvider } from "@/components/providers/AuthProvider";
 import { AboutPage } from "@/pages/AboutPage";
 import { ArtemisRequestPage } from "@/pages/ArtemisRequestPage";
+import { ExternalLinksAdminPage } from "@/pages/ExternalLinksAdminPage";
 import { ImprintPage } from "@/pages/ImprintPage";
 import { PrivacyPage } from "@/pages/PrivacyPage";
 import { StartPage } from "@/pages/StartPage";
@@ -36,6 +37,14 @@ function App() {
           />
           <Route path="/request/tum-guest" element={<TUMGuestRequestPage />} />
           <Route path="/request/support" element={<SupportRequestPage />} />
+          <Route
+            path="/admin/external-links"
+            element={
+              <ProtectedRoute requireAdmin>
+                <ExternalLinksAdminPage />
+              </ProtectedRoute>
+            }
+          />
           <Route path="/about" element={<AboutPage />} />
           <Route path="/privacy" element={<PrivacyPage />} />
           <Route path="/imprint" element={<ImprintPage />} />