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.

src/main/file_utils.ts

@@ -0,0 +1,16 @@
+import * as os from 'os';
+import * as path from 'path';
+
+export function expandPath(filePath: string): string {
+  if (!filePath) return filePath;
+  if (filePath.startsWith('[home]')) {
+    return path.join(os.homedir(), filePath.replace('[home]', ''));
+  }
+  return filePath;
+}
+
+export function getHashedPath(cacheRoot: string, hash: string): string {
+  const expandedRoot = expandPath(cacheRoot);
+  const subdirectory = hash.substring(0, 2);
+  return path.join(expandedRoot, subdirectory, `${hash}.file`);
+}