fix(security): medium/low — event-lock, atomic config, a11y, diashow, hygiene

- social: likes/comments rejected on a closed event (e2e proven).
- admin: patch_config validates-then-writes atomically; char-based length.
- hashtag/comment models: atomic tag writes in edit + comment paths.
- Modal: inert the background (modal-inert action) for screen readers.
- sse.ts: idempotent visibilitychange listener (no duplicate reconnects).
- diashow: videos advance on `ended` (transitions + page wiring).
- docs/hygiene: README clone-case fix; removed stale committed .env.test and
  gitignored it; docker-compose.dev.yml tidy.

Left documented as accepted-risk per plan: PIN-persist-after-logout,
UUID-reachable hidden uploads, DECISION-media-auth.md.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

e2e/specs/04-host/event-lock.spec.ts

@@ -33,4 +33,39 @@ test.describe('Host — event lock', () => {
     // Currently no UI consumes the event-closed SSE on /feed. Add this banner
     // and flip fixme to test once it lands.
   });
+
+  // Regression for the review: likes/comments used to ignore uploads_locked_at,
+  // so social writes still landed on a closed event. They now share the upload
+  // handler's lock guard.
+  test('a closed event rejects likes and comments', async ({ api, host, guest }) => {
+    const BASE = process.env.E2E_FRONTEND_URL ?? 'http://localhost:3101';
+    const g = await guest('SocialLocked');
+
+    // Upload while still open so there's a target to interact with.
+    const { uploadRaw } = await import('../../helpers/upload-client');
+    const { readFileSync } = await import('node:fs');
+    const { join } = await import('node:path');
+    const sample = join(process.cwd(), 'fixtures', 'media', 'sample.jpg');
+    const upRes = await uploadRaw(g.jwt, readFileSync(sample), {
+      filename: 'x.jpg',
+      contentType: 'image/jpeg',
+    });
+    expect(upRes.status).toBe(201);
+    const { id } = await upRes.json();
+
+    await api.closeEvent(host.jwt);
+
+    const likeRes = await fetch(`${BASE}/api/v1/upload/${id}/like`, {
+      method: 'POST',
+      headers: { Authorization: `Bearer ${g.jwt}` },
+    });
+    expect(likeRes.status).toBe(403);
+
+    const commentRes = await fetch(`${BASE}/api/v1/upload/${id}/comments`, {
+      method: 'POST',
+      headers: { Authorization: `Bearer ${g.jwt}`, 'Content-Type': 'application/json' },
+      body: JSON.stringify({ body: 'sollte blockiert sein' }),
+    });
+    expect(commentRes.status).toBe(403);
+  });
 });