Add pyproject.toml for consolidated project configuration and replace Black, isort, and Flake8 with Ruff

- Introduced `pyproject.toml` to centralize backend tool configurations (e.g., Ruff, mypy, coverage, pytest).
- Replaced Black, isort, and Flake8 with Ruff for linting, formatting, and import sorting.
- Updated `requirements.txt` to include Ruff and remove replaced tools.
- Added `Makefile` to streamline development workflows with commands for linting, formatting, type-checking, testing, and cleanup.

backend/app/models/base.py

@@ -1,20 +1,27 @@
 import uuid
-from datetime import datetime, timezone
+from datetime import UTC, datetime
 
 from sqlalchemy import Column, DateTime
 from sqlalchemy.dialects.postgresql import UUID
 
 # noinspection PyUnresolvedReferences
-from app.core.database import Base
 
 
 class TimestampMixin:
     """Mixin to add created_at and updated_at timestamps to models"""
-    created_at = Column(DateTime(timezone=True), default=lambda: datetime.now(timezone.utc), nullable=False)
-    updated_at = Column(DateTime(timezone=True), default=lambda: datetime.now(timezone.utc),
-                        onupdate=lambda: datetime.now(timezone.utc), nullable=False)
+
+    created_at = Column(
+        DateTime(timezone=True), default=lambda: datetime.now(UTC), nullable=False
+    )
+    updated_at = Column(
+        DateTime(timezone=True),
+        default=lambda: datetime.now(UTC),
+        onupdate=lambda: datetime.now(UTC),
+        nullable=False,
+    )
 
 
 class UUIDMixin:
     """Mixin to add UUID primary keys to models"""
+
     id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)