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>

tests/unit/middleware/test_context.py

@@ -10,13 +10,17 @@ Tests cover:
 - Edge cases and error handling
 """
 
-from unittest.mock import AsyncMock, Mock, patch
+from unittest.mock import AsyncMock, Mock
 
 import pytest
 from fastapi import Request
 
-from middleware.context import (ContextManager, ContextMiddleware,
-                                RequestContext, get_request_context)
+from middleware.context import (
+    ContextManager,
+    ContextMiddleware,
+    RequestContext,
+    get_request_context,
+)
 
 
 @pytest.mark.unit