Delete unused frontend UI files

[NoveliaYuki]

Removal of UI-related frontend and unused files

The knowledge base server will be completely backend, there won't be any UI because it is managed already in the LAMB frontend. To follow best practices, the follow will be deleted:

• lamb/lamb-kb-server-stable/frontend/ folder
• lamb/lamb-kb-server-stable/Dockerfile.webapp file
• lamb-kb-server-stable/backend/lamb_kb_webapp.py file
• lamb-kb-server-stable/backend/run_webapp.py file
• lamb-kb-server-stable/backend/templates/ folder