ref(backend): Centralize deps and add mypy

Extract reusable API dependencies and activity logging helpers.\nAdd mypy configuration and dev dependency for type checking.\n\nCo-Authored-By: Claude <noreply@anthropic.com>

backend/app/api/activity.py

@@ -1,13 +1,14 @@
 from __future__ import annotations
 
 from fastapi import APIRouter, Depends, Query
-from sqlmodel import Session, select
+from sqlalchemy import desc
+from sqlmodel import Session, col, select
 
-from app.core.auth import get_auth_context
+from app.api.deps import require_admin_auth
+from app.core.auth import AuthContext
 from app.db.session import get_session
 from app.models.activity_events import ActivityEvent
 from app.schemas.activity_events import ActivityEventRead
-from app.services.admin_access import require_admin
 
 router = APIRouter(prefix="/activity", tags=["activity"])
 
@@ -17,10 +18,12 @@ def list_activity(
     limit: int = Query(50, ge=1, le=200),
     offset: int = Query(0, ge=0),
     session: Session = Depends(get_session),
-    auth=Depends(get_auth_context),
+    auth: AuthContext = Depends(require_admin_auth),
 ) -> list[ActivityEvent]:
-    require_admin(auth)
     statement = (
-        select(ActivityEvent).order_by(ActivityEvent.created_at.desc()).offset(offset).limit(limit)
+        select(ActivityEvent)
+        .order_by(desc(col(ActivityEvent.created_at)))
+        .offset(offset)
+        .limit(limit)
     )
     return list(session.exec(statement))