feat(frontend): description field in task editor + Goal block in viewer

Note type gains description and consolidated_at fields. TaskEditorView
adds a Goal textarea above the body editor (wired through dirty/save/
autosave paths). TaskViewerView renders Goal as a subordinate block
above the body, plus a subtle 'Auto-summarized from work logs' banner
when consolidated_at is set.

Also adds a consolidateTask client function for the upcoming
re-consolidate button (Task 11).

frontend/src/views/TaskViewerView.vue

@@ -357,6 +357,22 @@ const subTaskProgress = computed(() => {
             @click="onTagClick"
           />
         </div>
+        <div
+          v-if="store.currentTask.description"
+          class="task-goal-display"
+        >
+          <h3 class="goal-label">Goal</h3>
+          <p class="goal-text">{{ store.currentTask.description }}</p>
+        </div>
+
+        <div
+          v-if="store.currentTask.consolidated_at"
+          class="auto-summary-banner"
+        >
+          <span class="auto-summary-icon" aria-hidden="true">✦</span>
+          Auto-summarized from work logs.
+        </div>
+
         <div
           class="body prose"
           v-html="renderedBody"
@@ -807,4 +823,42 @@ const subTaskProgress = computed(() => {
 .skel-line { height: 0.9rem; }
 .skel-line--short { width: 50%; }
 .skel-line--medium { width: 78%; }
+
+/* ── Goal block + auto-summary banner ─────────────────────────────────────── */
+.task-goal-display {
+  border-left: 2px solid var(--color-border, rgba(255, 255, 255, 0.12));
+  padding: 0.4rem 0 0.4rem 0.9rem;
+  margin: 0.75rem 0 1.25rem;
+  background: rgba(255, 255, 255, 0.02);
+}
+.goal-label {
+  font-family: var(--font-display, "Fraunces", serif);
+  font-style: italic;
+  font-size: 0.78rem;
+  font-weight: 500;
+  letter-spacing: 0.04em;
+  text-transform: uppercase;
+  color: var(--color-text-muted, rgba(255, 255, 255, 0.5));
+  margin: 0 0 0.25rem;
+}
+.goal-text {
+  margin: 0;
+  font-size: 0.95rem;
+  line-height: 1.45;
+  color: var(--color-text, inherit);
+  white-space: pre-wrap;
+}
+.auto-summary-banner {
+  display: flex;
+  align-items: center;
+  gap: 0.5rem;
+  font-size: 0.78rem;
+  font-style: italic;
+  color: var(--color-text-muted, rgba(255, 255, 255, 0.55));
+  margin: 0 0 0.75rem;
+}
+.auto-summary-icon {
+  color: var(--color-primary, #6366f1);
+  font-size: 0.85rem;
+}
 </style>