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>

app/api/v1/vendor/notifications.py

@@ -5,7 +5,6 @@ Vendor notification management endpoints.
 """
 
 import logging
-from typing import Optional
 
 from fastapi import APIRouter, Depends, Query
 from sqlalchemy.orm import Session
@@ -24,7 +23,7 @@ logger = logging.getLogger(__name__)
 def get_notifications(
     skip: int = Query(0, ge=0),
     limit: int = Query(50, ge=1, le=100),
-    unread_only: Optional[bool] = Query(False),
+    unread_only: bool | None = Query(False),
     vendor: Vendor = Depends(require_vendor_context()),
     current_user: User = Depends(get_current_vendor_api),
     db: Session = Depends(get_db),