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

server/utils/tokenStore.js

@@ -0,0 +1,83 @@
+/**
+ * Persistent token store backed by SQLite (better-sqlite3).
+ *
+ * Survives process restarts — Emby tokens remain valid across deploys
+ * and container restarts, so users do not need to re-login after an
+ * update. Tokens are stored in DATA_DIR/tokens.db (default: /app/data
+ * inside the container, or ./data locally).
+ *
+ * Schema: tokens(userId TEXT PK, accessToken TEXT, createdAt INTEGER)
+ *
+ * Expired rows (older than TOKEN_TTL_DAYS) are pruned on startup and
+ * once per hour, preventing unbounded growth.
+ */
+
+const Database = require('better-sqlite3');
+const path = require('path');
+const fs = require('fs');
+
+const TOKEN_TTL_DAYS = 31; // slightly longer than max cookie lifetime
+const DATA_DIR = process.env.DATA_DIR || path.join(__dirname, '../../data');
+
+// Ensure data directory exists (non-root writable in container)
+if (!fs.existsSync(DATA_DIR)) {
+  fs.mkdirSync(DATA_DIR, { recursive: true });
+}
+
+const DB_PATH = path.join(DATA_DIR, 'tokens.db');
+const db = new Database(DB_PATH);
+
+// WAL mode for better concurrent read performance
+db.pragma('journal_mode = WAL');
+db.pragma('foreign_keys = ON');
+
+db.exec(`
+  CREATE TABLE IF NOT EXISTS tokens (
+    userId      TEXT PRIMARY KEY,
+    accessToken TEXT NOT NULL,
+    createdAt   INTEGER NOT NULL DEFAULT (strftime('%s','now'))
+  )
+`);
+
+const storeToken = db.prepare(
+  `INSERT OR REPLACE INTO tokens (userId, accessToken, createdAt)
+   VALUES (?, ?, strftime('%s','now'))`
+);
+
+const getTokenStmt = db.prepare(
+  `SELECT accessToken FROM tokens WHERE userId = ?`
+);
+
+const clearTokenStmt = db.prepare(
+  `DELETE FROM tokens WHERE userId = ?`
+);
+
+const pruneStmt = db.prepare(
+  `DELETE FROM tokens WHERE createdAt < strftime('%s','now') - ?`
+);
+
+const TTL_SECONDS = TOKEN_TTL_DAYS * 24 * 60 * 60;
+
+function prune() {
+  const result = pruneStmt.run(TTL_SECONDS);
+  if (result.changes > 0) {
+    console.log(`[TokenStore] Pruned ${result.changes} expired token(s)`);
+  }
+}
+
+// Prune on startup and every hour
+prune();
+setInterval(prune, 60 * 60 * 1000).unref();
+
+module.exports = {
+  storeToken(userId, accessToken) {
+    storeToken.run(userId, accessToken);
+  },
+  getToken(userId) {
+    const row = getTokenStmt.get(userId);
+    return row ? { accessToken: row.accessToken } : null;
+  },
+  clearToken(userId) {
+    clearTokenStmt.run(userId);
+  }
+};