refactor: modernize code quality tooling with Ruff

- Replace black, isort, and flake8 with Ruff (all-in-one linter and formatter)
- Add comprehensive pyproject.toml configuration
- Simplify Makefile code quality targets
- Configure exclusions for venv/.venv in pyproject.toml
- Auto-fix 1,359 linting issues across codebase

Benefits:
- Much faster builds (Ruff is written in Rust)
- Single tool replaces multiple tools
- More comprehensive rule set (UP, B, C4, SIM, PIE, RET, Q)
- All configuration centralized in pyproject.toml
- Better import sorting and formatting consistency

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

middleware/rate_limiter.py

@@ -9,8 +9,7 @@ This module provides classes and functions for:
 
 import logging
 from collections import defaultdict, deque
-from datetime import datetime, timedelta, timezone
-from typing import Dict
+from datetime import UTC, datetime, timedelta
 
 logger = logging.getLogger(__name__)
 
@@ -21,9 +20,9 @@ class RateLimiter:
     def __init__(self):
         """Class constructor."""
         # Dictionary to store request timestamps for each client
-        self.clients: Dict[str, deque] = defaultdict(lambda: deque())
+        self.clients: dict[str, deque] = defaultdict(lambda: deque())
         self.cleanup_interval = 3600  # Clean up old entries every hour
-        self.last_cleanup = datetime.now(timezone.utc)
+        self.last_cleanup = datetime.now(UTC)
 
     def allow_request(
         self, client_id: str, max_requests: int, window_seconds: int
@@ -33,7 +32,7 @@ class RateLimiter:
 
         Uses sliding window algorithm
         """
-        now = datetime.now(timezone.utc)
+        now = datetime.now(UTC)
         window_start = now - timedelta(seconds=window_seconds)
 
         # Clean up old entries periodically
@@ -60,7 +59,7 @@ class RateLimiter:
 
     def _cleanup_old_entries(self):
         """Clean up old entries to prevent memory leaks."""
-        cutoff_time = datetime.now(timezone.utc) - timedelta(hours=24)
+        cutoff_time = datetime.now(UTC) - timedelta(hours=24)
 
         clients_to_remove = []
         for client_id, requests in self.clients.items():
@@ -80,11 +79,11 @@ class RateLimiter:
             f"Rate limiter cleanup completed. Removed {len(clients_to_remove)} inactive clients"
         )
 
-    def get_client_stats(self, client_id: str) -> Dict[str, int]:
+    def get_client_stats(self, client_id: str) -> dict[str, int]:
         """Get statistics for a specific client."""
         client_requests = self.clients.get(client_id, deque())
 
-        now = datetime.now(timezone.utc)
+        now = datetime.now(UTC)
         hour_ago = now - timedelta(hours=1)
         day_ago = now - timedelta(days=1)