Add ruff linter/formatter for Python

- Add ruff as dev dependency
- Configure ruff in pyproject.toml with strict 88-char line limit
- Ignore B008 (FastAPI Depends pattern is standard)
- Allow longer lines in tests for readability
- Fix all lint issues in source files
- Add Makefile targets: lint-backend, format-backend, fix-backend

backend/routes/audit.py

@@ -1,22 +1,23 @@
 """Audit routes for viewing action records."""
-from typing import Callable, TypeVar
+
+from collections.abc import Callable
+from typing import TypeVar
 
 from fastapi import APIRouter, Depends, Query
 from pydantic import BaseModel
-from sqlalchemy import select, func, desc
+from sqlalchemy import desc, func, select
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from auth import require_permission
 from database import get_db
-from models import User, SumRecord, CounterRecord, Permission
+from models import CounterRecord, Permission, SumRecord, User
 from schemas import (
     CounterRecordResponse,
-    SumRecordResponse,
     PaginatedCounterRecords,
     PaginatedSumRecords,
+    SumRecordResponse,
 )
 
-
 router = APIRouter(prefix="/api/audit", tags=["audit"])
 
 R = TypeVar("R", bound=BaseModel)