1.5.5

Remove Gemini API test button and Whisper mic test

- Remove Test connection button from onboarding API key screen
- Remove Whisper 5-second mic test panel and state from model-download screen
- Remove unused test-whisper-recording IPC handler, preload bridge, and speech.service method
- Keep model-download choice (now/later) and actual turbo weight download intact
- Downloaded turbo model is used for live speech without requiring user verification