feat: integrate Flask for serving backend and frontend

- Add Flask for serving both the backend and frontend of the application.
- Introduce app/generate_podcast.py for backend functionality.
- Delete app/keepyourmouthshut-api.py as it is no longer needed.
- Modify app/keepyourmouthshut.py to accommodate the changes.
- Rename assets/kyms-logo.png to app/static/kyms-logo.png for proper static file serving.
- Add app/templates/index.html for the main frontend template.
- Modify app/utils/edge_tts_stuff.py to reflect the changes.
- Delete infra/README.md as it is no longer relevant.
- Modify requirements.txt to include Flask as a dependency.