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/package.json

@@ -13,13 +13,13 @@
     "cookie-parser": "^1.4.7",
     "cors": "^2.8.5",
     "dotenv": "^16.3.1",
-    "express": "^4.18.2"
+    "express": "^4.18.2",
+    "tsx": "^4.19.0"
   },
   "devDependencies": {
     "@types/cookie-parser": "^1.4.10",
     "@types/cors": "^2.8.17",
     "@types/express": "^4.17.21",
-    "tsx": "^4.19.0",
     "typescript": "^5.9.3"
   }
 }