Remove remaining mongodb references

- Replace ObjectId import with string type in approval.workflow.ts
- Delete mongodb.d.ts type declaration file

Made-with: Cursor

GOOGLE_CLOUD_ENCOACH_ANALYSIS_CHAT.md

@@ -0,0 +1,8 @@
+# Google Cloud EnCoach Analysis
+
+Open this Cursor transcript using the chat UUID:
+
+- [Google Cloud EnCoach Analysis](9c3d1115-4845-4980-a0d5-33767025c260)
+
+Notes:
+- This is the transcript where `talal@encoach.com` was used for the Google Cloud EnCoach infrastructure analysis.