Refactor components to use ModalDialog and StatusMessage; update styles and remove unused files

- Replaced inline modal dialogs in ParentView with a reusable ModalDialog component.
- Introduced StatusMessage component for loading and error states in ParentView.
- Updated styles to use new colors.css and styles.css for consistent theming.
- Removed ChildRewardList.vue and ChildTaskList.vue components as they were no longer needed.
- Adjusted RewardAssignView and TaskAssignView to use new styles and shared button styles.
- Cleaned up imports across components to reflect the new styles and removed unused CSS files.

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

@@ -1,13 +1,28 @@
 <template>
   <div class="modal-backdrop">
     <div class="modal-dialog">
+      <div class="modal-heading">
+        <img v-if="imageUrl" :src="imageUrl" alt="Dialog Image" class="modal-image" />
+        <div class="modal-details">
+          <div class="modal-title">{{ title }}</div>
+          <div class="modal-subtitle">{{ subtitle }}</div>
+        </div>
+      </div>
       <slot />
     </div>
   </div>
 </template>
+
 <script setup lang="ts">
-// No script content needed unless you want to add props or logic
+import '@/assets/colors.css'
+
+defineProps<{
+  imageUrl?: string | null | undefined
+  title?: string
+  subtitle?: string | null | undefined
+}>()
 </script>
+
 <style scoped>
 .modal-backdrop {
   position: fixed;
@@ -22,11 +37,74 @@
   z-index: 1000;
 }
 .modal-dialog {
-  background: #fff;
+  background: var(--modal-bg, #fff);
   padding: 2rem;
   border-radius: 12px;
   box-shadow: 0 8px 32px rgba(0, 0, 0, 0.18);
   max-width: 340px;
   text-align: center;
 }
+.modal-image {
+  width: 72px;
+  height: 72px;
+  object-fit: cover;
+  border-radius: 8px;
+  background: var(--info-image-bg);
+}
+.modal-heading {
+  display: flex;
+  align-items: center;
+  gap: 1rem;
+  margin-bottom: 1rem;
+}
+.modal-details {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  margin: auto;
+}
+.modal-title {
+  font-weight: 600;
+  font-size: 1.1rem;
+}
+.modal-subtitle {
+  color: var(--info-points);
+  font-weight: 500;
+  font-size: 1rem;
+}
+
+/* Encapsulated slot content styles */
+.modal-message {
+  margin-bottom: 1.2rem;
+  font-size: 1rem;
+  color: var(--modal-message-color, #333);
+}
+
+:deep(.modal-actions) {
+  display: flex;
+  gap: 3rem;
+  justify-content: center;
+  margin-top: 0.5rem;
+}
+:deep(.modal-actions button) {
+  padding: 1rem 2.2rem;
+  border-radius: 12px;
+  border: 0;
+  cursor: pointer;
+  font-weight: 700;
+  font-size: 1.25rem;
+  transition: background 0.18s;
+  min-width: 120px;
+}
+
+@media (max-width: 480px) {
+  :deep(.modal-actions) {
+    gap: 1.2rem;
+  }
+  :deep(.modal-actions button) {
+    padding: 0.8rem 1.2rem;
+    font-size: 1.05rem;
+    min-width: 90px;
+  }
+}
 </style>