feat(FN-2592): add provider icons to task cards and detail modal

- Render provider icons on TaskCard model metadata with token-based sizing and spacing
- Add provider icon display in TaskDetailModal for executor, validator, and planning model rows
- Update dashboard styling with reusable provider icon classes and layout tweaks in component CSS
- Expand TaskCard tests to cover provider icon rendering and fallback behavior

packages/dashboard/app/components/TaskDetailModal.css

@@ -157,6 +157,12 @@
   margin-top: var(--space-lg);
 }
 
+.detail-provider-icons {
+  display: inline-flex;
+  align-items: center;
+  gap: var(--space-xs);
+}
+
 .detail-source-section {
   border: 1px solid var(--border);
   border-radius: var(--radius-md);