chore: complete CI migration and upgrade express to 5.2.0 (#321)

- Upgrade express from 5.1.0 to 5.2.0 (includes security fix for CVE-2024-51999)
- CI migration from CircleCI to GitHub Actions is complete:
  - GitHub Actions CI workflow implemented
  - GitHub Actions deployment workflow implemented
  - CircleCI configuration removed
  - README badges updated to GitHub Actions

Closes #281

Author: TooAngel

package-lock.json

@@ -34,7 +34,7 @@
     "@octokit/rest": "22.0.1",
     "@octokit/webhooks": "14.1.3",
     "connect-mongo": "5.1.0",
-    "express": "5.1.0",
+    "express": "5.2.0",
     "express-session": "1.18.2",
     "mongodb": "6.20.0",
     "node-cron": "4.2.1",