fix: Improve Whisper model status verification and PyInstaller builds

- Add robust model cache verification (check model.bin + config.json)
- Add new status messages: model_cached, incomplete_cache, model_error
- Forward model status events to frontend for better UI feedback
- Add clean_build_cache() to remove stale spec files before build
- Add --clean flag to PyInstaller commands
- Change sidecar from --onefile to --onedir for faster startup
- Add missing hidden imports: onnxruntime, wave, huggingface_hub.utils

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

client/src/main.js

@@ -423,6 +423,21 @@ function startSidecar() {
           if (msg.status === "model_loaded" && mainWindow) {
             mainWindow.webContents.send("model-download-progress", msg);
           }
+
+          // Forward model cached status (model was already downloaded)
+          if (msg.status === "model_cached" && mainWindow) {
+            mainWindow.webContents.send("model-download-progress", msg);
+          }
+
+          // Forward incomplete cache status
+          if (msg.status === "incomplete_cache" && mainWindow) {
+            mainWindow.webContents.send("model-download-progress", msg);
+          }
+
+          // Forward model error status
+          if (msg.status === "model_error" && mainWindow) {
+            mainWindow.webContents.send("model-download-progress", msg);
+          }
         } catch (e) {
           console.log("Sidecar output:", line);
         }