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/deps.py

@@ -0,0 +1,36 @@
+from __future__ import annotations
+
+from fastapi import Depends, HTTPException, status
+from sqlmodel import Session
+
+from app.core.auth import AuthContext, get_auth_context
+from app.db.session import get_session
+from app.models.boards import Board
+from app.models.tasks import Task
+from app.services.admin_access import require_admin
+
+
+def require_admin_auth(auth: AuthContext = Depends(get_auth_context)) -> AuthContext:
+    require_admin(auth)
+    return auth
+
+
+def get_board_or_404(
+    board_id: str,
+    session: Session = Depends(get_session),
+) -> Board:
+    board = session.get(Board, board_id)
+    if board is None:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND)
+    return board
+
+
+def get_task_or_404(
+    task_id: str,
+    board: Board = Depends(get_board_or_404),
+    session: Session = Depends(get_session),
+) -> Task:
+    task = session.get(Task, task_id)
+    if task is None or task.board_id != board.id:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND)
+    return task