chore: update CI workflows for validation, build and release

[MusicMaster4]

Summary

• Added transcription model selection to settings, allowing users to choose any available model from OpenRouter.
• Improved floating overlay interactions and polished the UI.
• Updated accessibility service to keep clipboard content.
• Improved audio capture validation and error handling.
• Stabilized Android audio recording.
• Adjusted icon insets to 16% for adaptive icons.
• Updated the GitHub Actions workflow to separate validation and build steps, improving the release process.
• Updated the README to reflect the new transcription model selection feature.
• Refactored FloatingOverlayService.kt to improve interactions and add a removal target for the floating bubble.
• Updated OpenFlowAccessibilityService.kt to keep clipboard content.
• Updated OpenFlowEngine.kt to handle new transcription model selection.
• Updated recording_service.dart to improve audio capture validation and error handling.
• Added new tests for the floating overlay and transcription features.

Test plan

• Verify that the transcription model can be selected and saved in the settings.
• Test the floating overlay interactions and ensure the removal target works correctly.
• Check that the clipboard content is preserved when using the accessibility service.
• Validate that audio capture works correctly and handles errors appropriately.
• Ensure that the Android audio recording is stable.
• Verify that the icon insets are correctly set to 16% for adaptive icons.
• Run the updated GitHub Actions workflow to ensure the validation and build steps work as expected.
• Check that the README accurately reflects the new transcription model selection feature.
• Run the new tests for the floating overlay and transcription features.