refactor: migrate project storage from IndexedDB to OPFS with folder-based structure

- Replace monolithic KGStorage with KGProjectStorage (OPFS) and KGConfigStorage (IndexedDB)
- Each project stored as folder: project.json + meta.json + media/
- Add KGConfigUpgrader with V1 upgrader to auto-migrate existing IndexedDB projects to OPFS
- Request persistent storage via navigator.storage.persist() to prevent browser eviction
- Show loading spinner during one-time migration
- Enforce safe project name characters (letters, numbers, space, hyphen, underscore, period, parens)
- Export projects as .kgstudio zip bundles instead of raw JSON
- Import supports .kgstudio bundles (with meta.json validation) and legacy JSON files
- Auto-deduplicate project names on import with (1), (2), etc. suffix
- Add OPFS shell debugger (pwd, ls, cd, cat, dl) accessible via KGDebugger.opfs()
- Add ESLint semi rule for consistent semicolons
- Delete KGStorage.ts — all logic absorbed by new storage classes
- Add jszip dependency for zip export/import

src/App.tsx

@@ -141,6 +141,9 @@ function App() {
 
       {/* Global Loading Overlay for instrument buffer loading */}
       <GlobalLoadingOverlayContainer />
+
+      {/* Migration Loading Overlay */}
+      <MigrationOverlayContainer />
     </div>
   );
 }
@@ -210,3 +213,22 @@ const GlobalLoadingOverlayContainer: React.FC = () => {
     />
   );
 };
+
+// Migration overlay — shown during one-time IndexedDB -> OPFS migration
+const MigrationOverlayContainer: React.FC = () => {
+  const [isMigrating, setIsMigrating] = useState<boolean>(() => KGCore.instance().getIsMigrating());
+
+  useEffectReact(() => {
+    KGCore.instance().setMigrationStateChangeCallback(setIsMigrating);
+    return () => {
+      KGCore.instance().setMigrationStateChangeCallback(() => {});
+    };
+  }, []);
+
+  return (
+    <LoadingOverlay
+      visible={isMigrating}
+      message="Migrating projects to new storage..."
+    />
+  );
+};