feat: deploy Express server via CI/CD with systemd + nginx proxy

- Update deploy.yml to rsync server/, install deps, write .env from
  Gitea secrets, and restart hihala-dashboard.service
- Move tsx to regular dependencies for production use
- Remove unused SESSION_SECRET from config
- Accept PORT env var as fallback for SERVER_PORT

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

server/src/config.ts

@@ -36,5 +36,4 @@ export const etl = {
 
 export const auth = {
   adminPin: process.env.ADMIN_PIN || '',
-  sessionSecret: process.env.SESSION_SECRET || 'hihala-dev-session-secret',
 };