Fix: Standardize Electron bridge and implement robust caching

- Refactored all IPC methods and parameters to snake_case for consistency with SvelteKit.
- Implemented exhaustive background caching engine with download locking.
- Reverted to legacy-proven flat hash storage pattern (hash.file).
- Added axios for reliable stream-based binary downloads.
- Updated preload and main handlers to support recursive room data fetching.

package.json

@@ -14,5 +14,8 @@
     "electron": "^34.0.0",
     "ts-node": "^10.9.2",
     "typescript": "^5.7.3"
+  },
+  "dependencies": {
+    "axios": "^1.13.2"
   }
-}
+}