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/theme_context.py

@@ -114,7 +114,7 @@ class ThemeContextMiddleware(BaseHTTPMiddleware):
                 request.state.theme = theme
 
                 logger.debug(
-                    f"[THEME] Theme loaded for vendor",
+                    "[THEME] Theme loaded for vendor",
                     extra={
                         "vendor_id": vendor.id,
                         "vendor_name": vendor.name,