feat: Implement user validation and ownership checks for image, reward, and task APIs

- Added `get_validated_user_id` utility function to validate user authentication across multiple APIs.
- Updated image upload, request, and listing endpoints to ensure user ownership and proper error handling.
- Enhanced reward management endpoints to include user validation and ownership checks.
- Modified task management endpoints to enforce user authentication and ownership verification.
- Updated models to include `user_id` for images, rewards, tasks, and children to track ownership.
- Implemented frontend changes to ensure UI reflects the ownership of tasks and rewards.
- Added a new feature specification to prevent deletion of system tasks and rewards.

backend/models/image.py

@@ -2,12 +2,14 @@
 from dataclasses import dataclass
 from models.base import BaseModel
 
+
 @dataclass
 class Image(BaseModel):
     type: int
     extension: str
     permanent: bool = False
-    user: str | None = None
+    user_id: str | None = None
+
 
     @classmethod
     def from_dict(cls, d: dict):
@@ -19,7 +21,7 @@ class Image(BaseModel):
             id=d.get('id'),
             created_at=d.get('created_at'),
             updated_at=d.get('updated_at'),
-            user=d.get('user')
+            user_id=d.get('user_id') if 'user_id' in d else d.get('user')
         )
 
     def to_dict(self):
@@ -28,6 +30,6 @@ class Image(BaseModel):
             'type': self.type,
             'permanent': self.permanent,
             'extension': self.extension,
-            'user': self.user
+            'user_id': self.user_id
         })
         return base