feat(FN-2624): surface task token usage on task cards

- Render a compact token usage indicator in TaskCard footer with accessible labeling and token-aware styling
- Track token usage fields in the TaskCard memo comparator and expose a comparator test helper for regression coverage
- Add TaskCard tests for token usage rendering behavior and comparator invalidation on token usage updates
- Configure runtime plugin Vitest setups with an @fusion/engine source alias for reliable workspace test resolution
- Keep restart integration child_process spawn mocking aligned with execSync-driven merge verification behavior

packages/dashboard/app/components/TaskCard.css

@@ -478,6 +478,21 @@
   opacity: 0.7;
 }
 
+.card-token-usage {
+  display: inline-flex;
+  align-items: center;
+  gap: var(--space-xs);
+  color: var(--text-muted);
+  font-size: calc(var(--space-sm) + var(--space-xs) * 0.75);
+  line-height: 1;
+  white-space: nowrap;
+}
+
+.card-token-usage-value {
+  font-family: var(--font-mono);
+  font-weight: 600;
+}
+
 .card-time-indicator {
   display: inline-flex;
   align-items: center;
@@ -982,6 +997,10 @@
     gap: var(--space-xs);
   }
 
+  .card-token-usage {
+    font-size: calc(var(--space-sm) + var(--space-xs) * 0.5);
+  }
+
   .card-time-indicator {
     padding: var(--space-xs) var(--space-sm);
     font-size: 10px;