fix: Resolve demo account login issues and Express trust proxy

- Enable database seeding (RUN_SEED: true) to create demo accounts
- Fix Express trust proxy configuration for nginx reverse proxy
- Add AGENTS.md with comprehensive development guidelines
- All demo accounts now working: admin, recruiter, employer, candidate
- Resolve rate limiting configuration warnings

Fixes: Demo account login failures, Express trust proxy errors

backend/src/server.js

@@ -15,6 +15,9 @@ const resumeRoutes = require('./routes/resumes');
 
 const app = express();
 
+// Trust proxy for nginx reverse proxy
+app.set('trust proxy', true);
+
 const authLimiter = rateLimit({
   windowMs: config.rateLimit.windowMs,
   max: config.rateLimit.max,