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.

frontend/vue-app/src/components/shared/LoginButton.vue

@@ -2,7 +2,12 @@
 import { ref, nextTick, onMounted, onUnmounted } from 'vue'
 import { useRouter } from 'vue-router'
 import { eventBus } from '@/common/eventBus'
-import { authenticateParent, isParentAuthenticated, logoutParent } from '../../stores/auth'
+import {
+  authenticateParent,
+  isParentAuthenticated,
+  logoutParent,
+  logoutUser,
+} from '../../stores/auth'
 import '@/assets/styles.css'
 import '@/assets/colors.css'
 import ModalDialog from './ModalDialog.vue'
@@ -91,7 +96,7 @@ function closeDropdown() {
 async function signOut() {
   try {
     await fetch('/api/logout', { method: 'POST' })
-    logoutParent()
+    logoutUser()
     router.push('/auth')
   } catch {
     // Optionally show error