docs: fact-check sweep, Jellyfin, *arr stack, and ROM scraping guides

Fact-check results:
- RomM 5.2.0: MariaDB+Redis now required (was SQLite), auth var renamed, 11 metadata providers
- Copyparty v1.20.19: 3 CVEs fixed, WOPI integration, docker editions documented
- Calibre-Web 0.6.27-ls397: version pinning, kepubify auto-config, CVE fixes
- Calibre 9.9.0: content server security fix noted

New documentation:
- docs/Dankserver/Jellyfin.md — full media server guide (compose, Caddy, GPU, metadata, clients)
- docs/Dankserver/ARR-Stack.md — automated download stack overview
- docs/Dankserver/RomM-Scraping.md — metadata providers, naming, cover art, emulator integration
- docs/Dankserver/sonarr.md, radarr.md, lidarr.md, readarr.md, prowlarr.md, qbittorrent.md
- docs/Dankserver/mariadb.md, redis.md — supporting services for RomM

Infrastructure updates:
- dankserver/compose.yaml: added mariadb, redis, jellyfin, *arr services
- dankserver/Caddyfile: added hostnames for all new services
- dankserver/.env.example: added all new environment variables
- docs/index.md: linked all new documentation pages

Tested: 52/52 tests pass.

docs/Dankserver/redis.md

@@ -0,0 +1,40 @@
+# Redis (RomM Cache / Queue)
+
+Redis 7 provides the caching and task queue backend for RomM on Dankserver. RomM 5.2.0 requires Redis (or Valkey) for its task queue.
+
+**Host:** Dankserver — **Docs:** https://redis.io/docs/
+
+## Facts
+
+| Item | Value |
+|------|-------|
+| Image | `docker.io/redis:7-alpine` |
+| Port | 6379 (internal, within `appnet`) |
+| Data volume | `/opt/romm/redis` |
+| Auth | None (local-only, no password needed) |
+
+## Docker Compose
+
+```yaml
+redis:
+  image: docker.io/redis:7-alpine
+  container_name: romm-redis
+  restart: unless-stopped
+  volumes:
+    - /opt/romm/redis:/data
+  healthcheck:
+    test: ["CMD", "redis-cli", "ping"]
+    interval: 10s
+    timeout: 5s
+    retries: 3
+```
+
+## Backup
+
+```bash
+sudo rsync -a /opt/romm/redis /mnt/backup/romm-redis/
+```
+
+## See Also
+
+- [[RomM]] — service that uses this cache