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/user.py

@@ -1,4 +1,4 @@
-from sqlalchemy import Column, String, Boolean, DateTime
+from sqlalchemy import Boolean, Column, DateTime, String
 from sqlalchemy.dialects.postgresql import JSONB
 from sqlalchemy.orm import relationship
 
@@ -6,7 +6,7 @@ from .base import Base, TimestampMixin, UUIDMixin
 
 
 class User(Base, UUIDMixin, TimestampMixin):
-    __tablename__ = 'users'
+    __tablename__ = "users"
 
     email = Column(String(255), unique=True, nullable=False, index=True)
     password_hash = Column(String(255), nullable=False)
@@ -19,7 +19,9 @@ class User(Base, UUIDMixin, TimestampMixin):
     deleted_at = Column(DateTime(timezone=True), nullable=True, index=True)
 
     # Relationships
-    user_organizations = relationship("UserOrganization", back_populates="user", cascade="all, delete-orphan")
+    user_organizations = relationship(
+        "UserOrganization", back_populates="user", cascade="all, delete-orphan"
+    )
 
     def __repr__(self):
-        return f"<User {self.email}>"
+        return f"<User {self.email}>"