style: apply black and isort formatting across entire codebase

- Standardize quote style (single to double quotes)
- Reorder and group imports alphabetically
- Fix line breaks and indentation for consistency
- Apply PEP 8 formatting standards

Also updated Makefile to exclude both venv and .venv from code quality checks.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

models/database/base.py

@@ -10,5 +10,8 @@ class TimestampMixin:
 
     created_at = Column(DateTime, default=datetime.now(timezone.utc), nullable=False)
     updated_at = Column(
-        DateTime, default=datetime.now(timezone.utc), onupdate=datetime.now(timezone.utc), nullable=False
+        DateTime,
+        default=datetime.now(timezone.utc),
+        onupdate=datetime.now(timezone.utc),
+        nullable=False,
     )