Fix bugs across AI dev assistant

[Xenon010101]

Summary

Fixed 5 bugs across the AI Dev Assistant codebase:

1. Debug console.log left in production (frontend)

File: frontend/index.html

• Removed console.log(entry) debug statement left in the loadEntry function.

2. Debug print() call left in backend

File: backend/app/utils/file_validator.py

• Removed print(f"Detected MIME Type: {detected_mime}") debugging statement.

3. Duplicate MIME type entries for .cpp

File: backend/app/utils/upload_config.py

• Removed duplicate entries in the .cpp allowed MIME types list.

4. Function name shadows imported class

File: backend/app/routers/upload_file.py

• Renamed upload_file handler to upload_file_route to avoid shadowing the UploadFile class import.

5. Incorrect return type annotations

File: backend/app/utils/file_validator.py

• Fixed validate_file_extension and validate_file return types from -> None to -> str

Fixes various bugs found during code review.

[imDarshanGK]

@Xenon010101 update your branch with the latest main changes, resolve conflicts and add issue number

[Xenon010101]

Hi @imDarshanGK, I have updated the branch with the latest main changes and resolved all conflicts. The PR is ready for re-review. Thanks!