feat: model management improvements and folder migration

- Add model folder migration with byte-level progress tracking (backend + UI)
- Custom models directory support via VOICEBOX_MODELS_DIR env var passed to sidecar
- Hardcoded model descriptions displayed in model detail cards
- Open model folder button in storage location row
- Remove 'not downloaded' badge from model cards
- Fix server settings scroll offset for audio player
- Fix shell open permission to allow file paths
- Add normalize toggle to generation settings

web/src/platform/lifecycle.ts

@@ -3,7 +3,7 @@ import type { PlatformLifecycle } from '@/platform/types';
 class WebLifecycle implements PlatformLifecycle {
   onServerReady?: () => void;
 
-  async startServer(_remote = false): Promise<string> {
+  async startServer(_remote = false, _modelsDir?: string | null): Promise<string> {
     // Web assumes server is running externally
     // Return a default URL - this should be configured via env vars
     const serverUrl = import.meta.env.VITE_SERVER_URL || 'http://localhost:17493';
@@ -15,7 +15,7 @@ class WebLifecycle implements PlatformLifecycle {
     // No-op for web - server is managed externally
   }
 
-  async restartServer(): Promise<string> {
+  async restartServer(_modelsDir?: string | null): Promise<string> {
     // No-op for web - server is managed externally
     return import.meta.env.VITE_SERVER_URL || 'http://localhost:17493';
   }