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.

src/transcription/AudioHandler.ts

@@ -30,7 +30,7 @@ export class AudioHandler {
 		}
 	}
 
-	private getTranscriptionApiKey(): string {
+	getTranscriptionApiKey(): string {
 		switch (this.plugin.settings.transcriptionProvider) {
 			case "groq":
 				return this.plugin.settings.groqApiKey;