Root cause: StaticFiles on '/' was blocking all /api/* requests
because it was defined BEFORE the API routes.
FastAPI routing rule: First match wins. StaticFiles with html=True
returns 404 for non-existent files instead of passing to next handler.
Fix: Move app.mount('/', StaticFiles(...)) to the END of main.py,
AFTER all @app.get/@app.post decorators.
fix: include missing system_metrics, cost_tracking, multi_agent routers
Problem: All API endpoints returned 404
Root cause: Router modules existed but were not included in main.py
Fix: Added app.include_router() for metrics, cost, and multi-agent routers
