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.

.github/specs/active/no-delete-system-tasks-and-rewards.md

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+# Feature: Do Not Allow System Tasks or System Rewards To Be Deleted
+
+## Context:
+
+- **Goal:** In Task List view and Reward List view, do not allow items to be deleted by the user if they are system tasks.
+- **User Story:** As a [user], I want to only be able to press the delete button on a task or reward if that item is not a system task or reward so that shared system tasks are not deleted for other users.
+
+## Technical Requirements
+
+- **File Affected:** ItemList.vue, TaskView.vue, RewardView.vue, task_api.py, reward_api.py
+- **Logic:**
+  1. Starting with ItemList.vue, we should check to see if any item in the list has an "user_id" property and if that property is null.
+  2. If the property is null, that means the item is not owned by a user, so do no display a delete button.
+  3. If the ItemList has it's deletable property as false, don't bother checking each item for user_id as the delete button will not display.
+  4. As a safeguard, on the backend, the DELETE api requests should check to see if the "user_id" property of the requested task or reward is null. This is done by requesting the item from the database. The request provides the item's id. If the item is a system item, return 403. Let the return tell the requestor that the item is a system item and cannot be deleted.
+  5. As a safeguard, make PUT/PATCH operations perform a copy-on-edit of the item. This is already implemented.
+  6. Bulk deletion is not possible, don't make changes for this.
+  7. For any item in the frontend or backend that does not have a "user_id" property, treat that as a system item (user_id=mull)
+  8. For both task and reward api create an application level constraint on the database that checks for user_id before mutation logic.
+
+## Acceptance Criteria (The "Definition of Done")
+
+- [ ] Logic: Task or Reward does not display the delete button when props.deletable is true and a list item is a system item.
+- [ ] UI: Doesn't show delete button for system items.
+- [ ] Backend Tests: Unit tests cover a delete API request for a system task or reward and returns a 403.
+- [ ] Frontend Tests: Add vitest for this feature in the frontend to make sure the delete button hidden or shown.