feat(FN-1066): add descriptions to agent presets and display in UI

- Add description field to all 20 agent presets in NewAgentDialog
- Display preset descriptions below role badge in preset selection cards
- Use preset description as agent title when selecting a preset
- Add CSS styling for description text with 2-line clamp
- Add tests verifying descriptions render, are non-empty, and populate title field

packages/dashboard/app/styles.css

@@ -21083,6 +21083,17 @@ html .column.drag-over * {
   text-transform: capitalize;
 }
 
+.agent-preset-description {
+  font-size: 11px;
+  color: var(--text-muted);
+  line-height: 1.3;
+  display: -webkit-box;
+  -webkit-line-clamp: 2;
+  -webkit-box-orient: vertical;
+  overflow: hidden;
+  margin-top: 2px;
+}
+
 .agent-dialog-required {
   color: var(--state-error-text);
 }