fix: Improve MCP fallback logic for STT service connection

- Fix HTTP fallback to properly return valid transcription results
- Remove immediate error return when ImportError occurs in MCP client
- Ensure WebSocket/HTTP STT services work when MCP is unavailable
- Addresses "ERROR: MCP STT service failed - no demo mode" issue
- Enables proper unmute.sh methodology with external STT services

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

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

core/mcp_audio_handler.py

@@ -369,7 +369,9 @@ class MCPAudioHandler:
                 
                 # Try HTTP fallback
                 if hasattr(self, 'stt_http_url') and self.stt_http_url:
-                    return await self._call_http_stt_service(audio_file_path)
+                    result = await self._call_http_stt_service(audio_file_path)
+                    if result and not result.startswith("Error"):
+                        return result
                 
                 # Return error - no simulation
                 return "ERROR: No STT services available"