feat(KB-624): add settings export and import functionality

- Add core settings export/import module with comprehensive tests
- Add CLI commands: kb settings --export and kb settings --import
- Add dashboard API endpoints for settings export/import
- Add dashboard UI for exporting and importing settings in SettingsModal
- Add changeset for @gsxdsm/fusion package release

packages/dashboard/app/styles.css

@@ -969,6 +969,28 @@ body {
   background: rgba(0, 0, 0, 0.05);
 }
 
+.modal-actions-left {
+  display: flex;
+  gap: 10px;
+  margin-right: auto;
+}
+
+.modal-actions-right {
+  display: flex;
+  gap: 10px;
+}
+
+.import-preview-list {
+  margin: 8px 0;
+  padding-left: 20px;
+  font-size: 12px;
+  color: var(--text-muted);
+}
+
+.import-preview-list li {
+  margin: 4px 0;
+}
+
 /* === Forms === */
 .form-group {
   padding: 0 var(--space-xl);