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>

README.md

@@ -94,9 +94,9 @@ eventsnap/
 ### Deploy on a fresh VPS
 
 ```bash
-# 1. Clone the repository
-git clone https://git.mc02.dev/fabi/EventSnap.git
-cd EventSnap
+# 1. Clone the repository (into a lowercase dir, matching the paths used below)
+git clone https://git.mc02.dev/fabi/EventSnap.git eventsnap
+cd eventsnap
 
 # 2. Configure environment
 cp .env.example .env