fix: check API key before starting recording

Previously the API key was only validated after stopping the
recording, wasting a full take if no key was configured. Now
startRecording() checks the transcription provider's API key
up front and aborts with a notice before touching the mic.

main.ts

@@ -89,6 +89,10 @@ export default class NibbleAI extends Plugin {
 			new Notice("Already recording");
 			return;
 		}
+		if (!this.audioHandler.getTranscriptionApiKey()) {
+			new Notice("✘ Add your API key for the selected transcription provider in NibbleAI settings");
+			return;
+		}
 		try {
 			await this.recorder.startRecording();
 			this.statusBar.updateStatus(RecordingStatus.Recording);