fix: voice input in Electron - local Whisper STT + network error handling

- Add local Whisper STT via Transformers.js with Web Worker (no UI freeze)
- Default sttProvider to 'local' in Electron (browser STT unavailable)
- Fix infinite toast loop: stop auto-restart on network errors
- Add retry limit with exponential backoff for transient STT errors
- Append voice transcript to input field (append-inline), not replace
- Add model catalog with download/load button in Voice Settings

packages/ui/src/lib/desktop.ts

@@ -166,9 +166,10 @@ export type DesktopSettings = {
   responseStyleEnabled?: boolean;
   responseStylePreset?: 'concise' | 'detailed' | 'mentor' | 'pushback' | 'noFiller' | 'matchEnergy' | 'warmPeer' | 'custom';
   responseStyleCustomInstructions?: string;
-  sttProvider?: 'browser' | 'server';
+  sttProvider?: 'browser' | 'server' | 'wasm';
   sttServerUrl?: string;
   sttModel?: string;
+  wasmSttModel?: string;
   sttLanguage?: string;
   sttSilenceThresholdDb?: number;
   sttSilenceHoldMs?: number;