restore: Bring back full VoiceCal WebRTC interface

debug: Switch to ultra-minimal Streamlit test to isolate restart loop issue

debug: Simplify VoiceCal to isolate restart issue cause

refactor: Streamline VoiceCal to pure WebSocket connectivity with STT v1.0.0

fix: Switch to Gradio HTTP API fallback for WebSocket connectivity issues

fix: Update WebSocket URL to /api/ws/stt to avoid Gradio routing conflicts

fix: Simplify VoiceCal to single Streamlit service with direct STT connection