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>

models/schema/__init__.py

@@ -2,8 +2,16 @@
 """API models package - Pydantic models for request/response validation."""
 
 # Import API model modules
-from . import (auth, base, inventory, marketplace_import_job,
-               marketplace_product, stats, vendor)
+from . import (
+    auth,
+    base,
+    inventory,
+    marketplace_import_job,
+    marketplace_product,
+    stats,
+    vendor,
+)
+
 # Common imports for convenience
 from .base import *  # Base Pydantic models