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/core/lifespan.py

@@ -16,7 +16,7 @@ from sqlalchemy import text
 
 from middleware.auth import AuthManager
 
-from .database import SessionLocal, engine
+from .database import engine
 from .logging import setup_logging
 
 # Remove this import if not needed: from models.database.base import Base
@@ -60,7 +60,6 @@ def check_database_ready():
 def get_migration_status():
     """Get current Alembic migration status."""
     try:
-        from alembic import command
         from alembic.config import Config
 
         alembic_cfg = Config("alembic.ini")