Feature/waveform issue 2

[fbraza]

Summary

• Build out the live waveform visualization (lib/features/voice_to_text/widget/waveform.dart) with smoothing
  animation, stream wrapper, and bar styling that matches the design guide.
• Extend VoiceToTextModelState (lib/features/voice_to_text/view/voice_to_text_model.dart) to track waveform samples/stream and update the voice screen to render the widget with temporary mock data (lib/features/voice_to_text/view/voice_to_text_screen.dart).
• Cover the new logic with unit/widget tests (test/features/voice_to_text/view/voice_to_text_model_test.dart, test/ features/voice_to_text/widget/waveform_test.dart).
• Document project conventions in AGENTS.md so contributors have a concise onboarding reference.
• Add .github/workflows/CI.yml to run flutter pub get and flutter test on pushes and PRs via subosito/flutter- action.

Testing

• flutter test

[fbraza]

solves #2