Task views: same UI refinement pass as note views

TaskEditorView:
- Back button standardized to "← Tasks"
- Toolbar now on same row as Write/Preview tabs (flex-direction row)
- Save button and title input inherit gradient/Fraunces from editor-shared.css

TaskViewerView:
- Shimmer skeleton loader replaces plain "Loading..." text
- Task title uses Fraunces font at 2rem
- Edit button becomes primary gradient CTA
- Meta timestamps show clock/pencil SVG icons
- Backlinks section: card grid with colored type badges (note=indigo, task=amber)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/views/TaskEditorView.vue

@@ -382,7 +382,7 @@ useEditorGuards(dirty, save);
   <main class="editor-page task-editor-page">
     <div class="editor-header">
       <div class="toolbar">
-        <router-link to="/tasks" class="btn-back">Back</router-link>
+        <router-link to="/tasks" class="btn-back">← Tasks</router-link>
         <button class="btn-save" @click="save" :disabled="saving">
           {{ saving ? "Saving..." : "Save" }}
         </button>
@@ -687,8 +687,12 @@ useEditorGuards(dirty, save);
 
 .body-tabs-row {
   display: flex;
-  flex-direction: column;
-  gap: 0.25rem;
+  flex-direction: row;
+  align-items: center;
+  gap: 0.75rem;
+  flex-wrap: wrap;
+  padding-bottom: 0.5rem;
+  border-bottom: 1px solid var(--color-border);
 }
 
 .body-editor-wrap {