refactor: modularize chat backend, update docs for .m4s segments

SETUP.md

@@ -223,7 +223,7 @@ flowchart LR
    - Use Cloudflare proxied DNS with Full (strict) TLS so browser traffic uses `https://linearvoid.tv`, `wss://linearvoid.tv/ws`, and `https://media.linearvoid.tv`.
 
 6. **Apply cache behavior**:
-   - Configure the `.ts` and `.m3u8` cache rules from `infrastructure/cloudflare/cache-rules.md`.
+   - Configure the `.m4s` and `.m3u8` cache rules from `infrastructure/cloudflare/cache-rules.md`.
    - Enable Smart Tiered Cache for the R2-backed hostname.
    - If you need header normalization for immutable segment caching, deploy `infrastructure/cloudflare/worker.js` to the same zone.
 
@@ -235,6 +235,8 @@ flowchart LR
 
 Use this section for full edge setup (DNS, Pages, cache, security, and monitoring).
 
+Execution tracker: `docs/operations/cloudflare-uptimerobot-checklist.md`.
+
 ### 1. DNS Setup
 
 1. Add apex record for `linearvoid.tv` pointing to Cloudflare Pages target.
@@ -262,7 +264,12 @@ Configure Cloudflare Cache Rules:
    - Cache: eligible
    - Edge TTL: `2s`
    - Revalidation: enabled
-3. Validate behavior using response headers:
+3. Static assets (`*.js`, `*.css`):
+   - Cache: eligible
+   - Edge TTL: `1y`
+   - Browser TTL: long-lived
+   - Cache key: include full path
+4. Validate behavior using response headers:
    - `Cf-Cache-Status` should move from `MISS` to `HIT` for hot objects
 
 Reference: `infrastructure/cloudflare/cache-rules.md`.
@@ -564,7 +571,7 @@ See `docs/architecture/README.md` for the full arc42 documentation and the ADRs
 - **R2 Upload Fails**: Check credentials in `.env` and ensure the bucket exists. Verify with `aws s3 ls --endpoint-url=$R2_ENDPOINT`.
 - **Normalization Errors**: Run `backend/playout/start-playout.sh` manually to see ffprobe output. All videos must be H.264/AAC, 30 fps constant, 2s keyframes (ADR-001).
 - **Chat Not Connecting**: Check Redis connection and WebSocket URL. The health check at `/health` should return 200.
-- **Cache Not Working**: Verify Cloudflare cache rules (`.ts` = long TTL immutable, `.m3u8` = short TTL). Check cache hit ratio in Cloudflare dashboard.
+- **Cache Not Working**: Verify Cloudflare cache rules (`.m4s` = long TTL immutable, `.m3u8` = short TTL). Check cache hit ratio in Cloudflare dashboard.
 - **Docker Issues**: Run `docker compose logs` for service-specific errors. Ensure ports are not in use.
 - **Admin Interface**: Ensure `ADMIN_USERNAME`, `ADMIN_PASSWORD`, and `ADMIN_SESSION_TTL_HOURS` are set. `/admin/` and `/api/admin/*` are protected by a session-based login flow.
 - **Production Pull Fails**: Confirm `docker login` to Gitea succeeded on the server and the image tags referenced by `docker-compose.prod.yml` exist.