fix(security): pre-launch security hardening audit & remediation (#320)

- Webhook HMAC: capture raw request bytes via express.json verify callback
  instead of re-serializing with JSON.stringify
- AES-256-GCM: use NIST-recommended 12-byte IV (backward compatible with
  existing 16-byte IVs)
- Node proxy tokens: add 1-year default expiry (previously no expiry)
- Host console env filtering: pattern-based approach blocking SECRET,
  PASSWORD, TOKEN, KEY, CREDENTIAL keywords (previously only 4 explicit keys)
- CORS: deny cross-origin requests when FRONTEND_URL is unset in production
  (previously fell back to allowing all origins)

backend/src/services/HostTerminalService.ts

@@ -18,9 +18,14 @@ export class HostTerminalService {
 
         // Strip sensitive backend secrets from the PTY environment so they are not
         // visible to the console user via `env` / `printenv`.
-        const SENSITIVE_KEYS = ['JWT_SECRET', 'AUTH_PASSWORD', 'AUTH_PASSWORD_HASH', 'DATABASE_URL'];
+        // Pattern-based filtering: block any env var containing sensitive keywords.
+        // Explicit fallback set catches vars that don't match patterns (e.g. DATABASE_URL).
+        const SENSITIVE_PATTERNS = /SECRET|PASSWORD|TOKEN|KEY|CREDENTIAL/i;
+        const SENSITIVE_KEYS = new Set(['DATABASE_URL']);
         const safeEnv = Object.fromEntries(
-            Object.entries(process.env as Record<string, string>).filter(([k]) => !SENSITIVE_KEYS.includes(k))
+            Object.entries(process.env as Record<string, string>).filter(
+                ([k]) => !SENSITIVE_PATTERNS.test(k) && !SENSITIVE_KEYS.has(k)
+            )
         );
 
         const ptyProcess = pty.spawn(shell, [], {