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/constants/coreConstants.ts

@@ -93,6 +93,18 @@ export const SAMPLER_CONSTANTS = {
   }, 
 };
 
+export const OPFS_CONSTANTS = {
+  ROOT_DIR: 'projects',
+  PROJECT_FILE: 'project.json',
+  METADATA_FILE: 'meta.json',
+  MEDIA_DIR: 'media',
+};
+
+export const CONFIG_UPGRADER_CONSTANTS = {
+  VERSION_KEY: '__config_version',
+  CURRENT_VERSION: 1,
+};
+
 export const URL_CONSTANTS = {
   DEFAULT_OPENAI_BASE_URL: 'https://api.openai.com/v1',
 };