Problem

The knowledge_learning router (deeptutor/api/routers/knowledge_learning.py) exists but is never imported or registered in deeptutor/api/main.py. All knowledge-learning API endpoints return 404.

Steps to Reproduce

1. Start the backend server
2. Call any /api/v1/knowledge-learning/ endpoint (e.g., GET /api/v1/knowledge-learning/documents)
3. Returns 404

Expected

The knowledge-learning endpoints should be accessible.

Fix

In main.py, add the import and router registration:

# In the router imports block (~line 267)
from deeptutor.api.routers import (
    ...
    knowledge_learning,
    ...
)

# In the router registration block (~line 310)
app.include_router(
    knowledge_learning.router,
    prefix="/api/v1/knowledge-learning",
    tags=["knowledge-learning"],
    dependencies=_auth,
)

Environment

• Python 3.14, Windows 11, latest main branch