Security hardening: go-live review fixes

- TV tokens upgraded from 4 to 6 digits; Regen Token button in Admin
- Nginx rate limiting on TV dashboard and WebSocket endpoints
- Login lockout after 5 failed attempts (15 min); clears on admin password reset
- HSTS header added; CSP unsafe-inline removed from script-src; CORS restricted to explicit methods/headers
- Dependency CVE fixes: PyJWT 2.12.0, aiomysql 0.3.0, cryptography 46.0.5, python-multipart 0.0.22
- datetime.utcnow() replaced with datetime.now(timezone.utc) throughout
- SQL identifier whitelist for startup migration queries
- README updated: security notes section, lockout docs, token regen, NPM proxy guidance

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/nginx.conf

@@ -1,8 +1,46 @@
+# Rate limiting zones — included inside http{} block
+limit_req_zone $binary_remote_addr zone=auth_limit:10m rate=5r/m;
+limit_req_zone $binary_remote_addr zone=tv_limit:10m rate=10r/m;
+
 server {
     listen 80;
+    server_tokens off;
     root /usr/share/nginx/html;
     index index.html;
 
+    # Security headers
+    add_header X-Frame-Options "SAMEORIGIN" always;
+    add_header X-Content-Type-Options "nosniff" always;
+    add_header X-XSS-Protection "1; mode=block" always;
+    add_header Referrer-Policy "strict-origin-when-cross-origin" always;
+    add_header Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'; img-src 'self' data: blob:; connect-src 'self' ws: wss:; font-src 'self' data:;" always;
+    add_header Strict-Transport-Security "max-age=31536000; includeSubDomains" always;
+
+    # Gzip compression
+    gzip on;
+    gzip_types text/plain text/css application/javascript application/json application/x-javascript text/xml application/xml;
+    gzip_min_length 1024;
+
+    # Rate-limited auth endpoints (checked before the generic /api/ block)
+    location ~ ^/api/(auth/(login|register)|admin/login)$ {
+        limit_req zone=auth_limit burst=3 nodelay;
+        limit_req_status 429;
+        proxy_pass http://backend:8000;
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+    }
+
+    # Rate-limited TV dashboard endpoint (public, token-based)
+    location ~ ^/api/dashboard/ {
+        limit_req zone=tv_limit burst=5 nodelay;
+        limit_req_status 429;
+        proxy_pass http://backend:8000;
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+    }
+
     # API proxy → FastAPI backend
     location /api/ {
         proxy_pass http://backend:8000;
@@ -13,6 +51,8 @@ server {
 
     # WebSocket proxy → FastAPI backend
     location /ws/ {
+        limit_req zone=tv_limit burst=5 nodelay;
+        limit_req_status 429;
         proxy_pass http://backend:8000;
         proxy_http_version 1.1;
         proxy_set_header Upgrade $http_upgrade;