fix: Improve Whisper model status error handling

- Set sidecarReady to false when model_error is received
- Store error message in activeWhisperConfig for status display
- Update frontend to show error state with red indicator
- Prevents showing ✅ when model failed to load

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

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

client/src/main.js

@@ -434,9 +434,15 @@ function startSidecar() {
             mainWindow.webContents.send("model-download-progress", msg);
           }
 
-          // Forward model error status
-          if (msg.status === "model_error" && mainWindow) {
-            mainWindow.webContents.send("model-download-progress", msg);
+          // Forward model error status and mark sidecar as not ready
+          if (msg.status === "model_error") {
+            sidecarReady = false;
+            if (activeWhisperConfig) {
+              activeWhisperConfig.error = msg.error || "Model load failed";
+            }
+            if (mainWindow) {
+              mainWindow.webContents.send("model-download-progress", msg);
+            }
           }
         } catch (e) {
           console.log("Sidecar output:", line);