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/types/opfs.d.ts

@@ -0,0 +1,9 @@
+/**
+ * Type augmentations for the Origin Private File System (OPFS) async iterable APIs.
+ * These are part of the File System Access API but not yet fully typed in TypeScript's lib.dom.d.ts.
+ */
+interface FileSystemDirectoryHandle {
+  values(): AsyncIterableIterator<FileSystemDirectoryHandle | FileSystemFileHandle>;
+  keys(): AsyncIterableIterator<string>;
+  entries(): AsyncIterableIterator<[string, FileSystemDirectoryHandle | FileSystemFileHandle]>;
+}