feat(security): production hardening for external deployment

Container (Dockerfile):
- Multi-stage build (deps + runtime) for minimal attack surface
- Upgrade base image from node:18-alpine to node:22-alpine
- Run as non-root 'node' user (UID 1000); source files owned by root
- /app/data directory owned by node for SQLite + logs
- Docker HEALTHCHECK: wget /health every 30s

docker-compose.yaml:
- Port bound to 127.0.0.1 only (expose via reverse proxy)
- read_only: true filesystem; /tmp tmpfs for Node.js
- no-new-privileges:true, cap_drop: ALL
- Named volume sofarr-data for persistent data
- TRUST_PROXY, COOKIE_SECRET, NODE_ENV added

Helmet v7 + CSP nonce:
- Upgrade helmet@4 → helmet@7, express-rate-limit@6 → @7
- CSP with per-request nonce injected into index.html script/link tags
  (replaces blanket unsafe-inline; nonce changes every request)
- HSTS: max-age=1yr, includeSubDomains, preload
- Referrer-Policy: strict-origin-when-cross-origin
- Permissions-Policy: camera/mic/geolocation/payment/usb all off
- index.html served dynamically with nonce injection; static assets
  served normally via express.static({index:false})

Trust proxy:
- TRUST_PROXY env var configures app.set('trust proxy') so rate
  limiting and secure cookies work correctly behind Nginx/Caddy

Session & auth:
- Token store migrated from in-memory Map to SQLite via better-sqlite3
  (server/utils/tokenStore.js): survives restarts, WAL mode, 31-day TTL
- CSRF double-submit cookie pattern (server/middleware/verifyCsrf.js):
  POST/PUT/PATCH/DELETE on /api/* require X-CSRF-Token header matching
  the csrf_token cookie; timing-safe comparison
- CSRF token issued on login + GET /api/auth/csrf; cleared on logout
- Login input validation: username/password length + type checked before
  hitting Emby
- skipSuccessfulRequests:true on login rate limiter (only count failures)
- express.json({ limit: '64kb' }) to reject oversized payloads

Rate limiting:
- General API limiter: 300 req/15min per IP on all /api/* routes
- Login limiter unchanged (10 failures/15min) but now only counts fails

Logging:
- Log file moved from /app/server.log to DATA_DIR/server.log (writable
  by non-root node user in container)
- Size-based rotation: rotate at 10 MB, keep 3 files (server.log.1-3)
- DATA_DIR defaults to ./data locally, /app/data in container

Error handling:
- Global Express error handler: catches unhandled errors, logs message,
  returns generic 500 (no stack traces to clients)

Health/readiness:
- GET /health: returns {status:'ok', uptime:N} — used by HEALTHCHECK
- GET /ready: returns 503 if EMBY_URL not configured

Error sanitization (sanitizeError.js):
- Added patterns for password= params, bearer tokens, Basic auth in URLs

Supply chain:
- Remove unused cors dependency
- add better-sqlite3@^9
- CI: upgrade to Node 22, raise audit level to --audit-level=high
- .gitignore: add data/, *.db, *.db-wal, *.db-shm

Docs:
- SECURITY.md: threat model, hardening checklist, proxy examples,
  header table, rate limit table, Docker secrets guidance
- .env.example + .env.sample: TRUST_PROXY, DATA_DIR documented

package.json

@@ -7,17 +7,18 @@
     "dev": "nodemon server/index.js",
     "start": "node server/index.js",
     "install:all": "npm install",
-    "audit": "npm audit --audit-level=moderate",
-    "audit:fix": "npm audit fix"
+    "audit": "npm audit --audit-level=high",
+    "audit:fix": "npm audit fix",
+    "audit:critical": "npm audit --audit-level=critical"
   },
   "dependencies": {
     "axios": "^1.6.0",
+    "better-sqlite3": "^9.0.0",
     "cookie-parser": "^1.4.6",
-    "cors": "^2.8.5",
     "dotenv": "^16.3.1",
     "express": "^4.18.2",
-    "express-rate-limit": "^6.7.0",
-    "helmet": "^4.6.0"
+    "express-rate-limit": "^7.0.0",
+    "helmet": "^7.0.0"
   },
   "devDependencies": {
     "concurrently": "^7.6.0",