Show loading spinner while model initializes

[rakendd]

Summary

• The record button is silently disabled while the Whisper model loads (isLoading=true), but shows no visual feedback — it looks like a normal clickable button
• This causes confusion for users, especially with larger models like large-v3-turbo (1.5GB) which take ~30 seconds to load
• Fix: add viewModel.transcriptionService.isLoading to the spinner condition so the loading indicator is shown during model initialization

Change

One-line change in ContentView.swift:

// Before:
if viewModel.state == .decoding || viewModel.state == .connecting {

// After:
if viewModel.state == .decoding || viewModel.state == .connecting || viewModel.transcriptionService.isLoading {

Test plan

• Launch app with a large model (e.g., large-v3-turbo)
• Verify spinner appears on the record button while model loads
• Verify spinner disappears and button becomes clickable once model is ready
• Verify normal recording/transcription flow still works

[Starmel]

The app displays a model loading indicator. What is the purpose of the progress bar on the button, which is blocked during loading and while the loading indicator is already displayed on the screen?