Enhance user management, improve API structure, add database optimizations, and update Docker setup

- Introduced endpoints for user management, including CRUD operations, pagination, and password management.
- Added new schema validations for user updates, password strength, pagination, and standardized error responses.
- Integrated custom exception handling for a consistent API error experience.
- Refined CORS settings: restricted methods and allowed headers, added header exposure, and preflight caching.
- Optimized database: added indexes on `is_active` and `is_superuser` fields, updated column types, enforced constraints, and set defaults.
- Updated `Dockerfile` to improve security by using a non-root user and adding a health check for the application.
- Enhanced tests for database initialization, user operations, and exception handling to ensure better coverage.

backend/app/schemas/users.py

@@ -123,7 +123,26 @@ class TokenData(BaseModel):
     is_superuser: bool = False
 
 
+class PasswordChange(BaseModel):
+    """Schema for changing password (requires current password)."""
+    current_password: str
+    new_password: str
+
+    @field_validator('new_password')
+    @classmethod
+    def password_strength(cls, v: str) -> str:
+        """Basic password strength validation"""
+        if len(v) < 8:
+            raise ValueError('Password must be at least 8 characters')
+        if not any(char.isdigit() for char in v):
+            raise ValueError('Password must contain at least one digit')
+        if not any(char.isupper() for char in v):
+            raise ValueError('Password must contain at least one uppercase letter')
+        return v
+
+
 class PasswordReset(BaseModel):
+    """Schema for resetting password (via email token)."""
     token: str
     new_password: str