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/database/base.py

@@ -1,17 +1,15 @@
-from datetime import datetime, timezone
+from datetime import UTC, datetime
 
 from sqlalchemy import Column, DateTime
 
-from app.core.database import Base
-
 
 class TimestampMixin:
     """Mixin to add created_at and updated_at timestamps to models"""
 
-    created_at = Column(DateTime, default=datetime.now(timezone.utc), nullable=False)
+    created_at = Column(DateTime, default=datetime.now(UTC), nullable=False)
     updated_at = Column(
         DateTime,
-        default=datetime.now(timezone.utc),
-        onupdate=datetime.now(timezone.utc),
+        default=datetime.now(UTC),
+        onupdate=datetime.now(UTC),
         nullable=False,
     )