fix: production JSON parsing errors and trust proxy issue

- Set Express to trust proxy headers for proper IP detection with Traefik
- Add safe JSON parsing for email template variables and activity log metadata
- Create migration to fix invalid JSON data in database
- Add error handling to prevent JSON.parse crashes

This fixes the 500 errors caused by invalid JSON data and the trust proxy
warning from express-rate-limit when running behind Traefik.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

backend/server.js

@@ -28,6 +28,9 @@ const adminAuthRoutes = require('./src/routes/adminAuth');
 const app = express();
 const PORT = process.env.PORT || 3000;
 
+// Trust proxy headers (required for Traefik/nginx)
+app.set('trust proxy', true);
+
 // Security middleware with custom CSP
 app.use(helmet({
   contentSecurityPolicy: {