Add organization management and admin-specific APIs

- Introduced schemas for organizations, including creation, updates, and responses.
- Created models for `Organization` and `UserOrganization` with role-based access control and relationships.
- Implemented admin APIs for managing users, organizations, and bulk actions.
- Added advanced filtering, sorting, and pagination for user and organization queries.
- Updated `CRUD` logic to support organization-specific operations and member management.
- Enhanced database with necessary indexes and validation for improved performance and data integrity.

backend/app/models/user.py

@@ -1,5 +1,6 @@
 from sqlalchemy import Column, String, Boolean, DateTime
 from sqlalchemy.dialects.postgresql import JSONB
+from sqlalchemy.orm import relationship
 
 from .base import Base, TimestampMixin, UUIDMixin
 
@@ -17,5 +18,8 @@ class User(Base, UUIDMixin, TimestampMixin):
     preferences = Column(JSONB)
     deleted_at = Column(DateTime(timezone=True), nullable=True, index=True)
 
+    # Relationships
+    user_organizations = relationship("UserOrganization", back_populates="user", cascade="all, delete-orphan")
+
     def __repr__(self):
         return f"<User {self.email}>"