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>

docker-compose.dev.yml

@@ -6,3 +6,8 @@ services:
   db:
     ports:
       - "5432:5432"
+  app:
+    # Relax the production secret guard for local dev — the dev sentinel JWT_SECRET
+    # is tolerated (warned) rather than rejected.
+    environment:
+      APP_ENV: development