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

public/app.js

@@ -4,6 +4,7 @@ let refreshInterval = null;
 let currentRefreshRate = 5000; // default 5 seconds
 let isAdmin = false;
 let showAll = false;
+let csrfToken = null; // double-submit CSRF token, sent as X-CSRF-Token on mutating requests
 const SPLASH_MIN_MS = 1200; // minimum splash display time
 
 // Apply saved theme immediately (before DOMContentLoaded to avoid flash)
@@ -118,9 +119,15 @@ function dismissSplash(startTime) {
 async function checkAuthentication() {
   const splashStart = Date.now();
   try {
-    const response = await fetch('/api/auth/me');
-    const data = await response.json();
-    
+    // Fetch both auth state and a fresh CSRF token in parallel
+    const [meRes, csrfRes] = await Promise.all([
+      fetch('/api/auth/me'),
+      fetch('/api/auth/csrf')
+    ]);
+    const data = await meRes.json();
+    const csrfData = await csrfRes.json();
+    if (csrfData.csrfToken) csrfToken = csrfData.csrfToken;
+
     if (data.authenticated) {
       currentUser = data.user;
       isAdmin = !!data.user.isAdmin;
@@ -160,6 +167,8 @@ async function handleLogin(e) {
     if (data.success) {
       currentUser = data.user;
       isAdmin = !!data.user.isAdmin;
+      // Store CSRF token returned by login for use in subsequent requests
+      if (data.csrfToken) csrfToken = data.csrfToken;
       // Fade out login, then show splash while loading data.
       // requestAnimationFrame ensures the browser paints the splash at
       // opacity:1 before dismissSplash adds fade-out, so the CSS
@@ -185,9 +194,11 @@ async function handleLogout() {
   try {
     stopAutoRefresh();
     await fetch('/api/auth/logout', {
-      method: 'POST'
+      method: 'POST',
+      headers: csrfToken ? { 'X-CSRF-Token': csrfToken } : {}
     });
     currentUser = null;
+    csrfToken = null;
     downloads = [];
     showLogin();
   } catch (err) {