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Summary

Adds a Test button to the Sound Output settings page to verify audio output devices are working. This feature was available in GNOME Settings but missing in COSMIC Settings (issue #1901).

Before

• Users had no built-in way to test if their selected output device was working
• Had to rely on external applications or media playback to verify audio output
• No feedback mechanism to confirm the correct device was selected

After

• Added a Test button next to the Output device dropdown
• Button is enabled only when an active output sink is available
• Clicking the button plays a test sound through the currently selected output device
• Multiple fallback playback methods ensure compatibility across different system configurations

Technical Details

UI Changes:

• Added TestOutput message variant to the Sound page message enum
• Test button appears inline with the Output device selector
• Button is disabled when no active sink is available

Backend Implementation:

• Model::test_output() spawns async playback task
• Fallback chain for maximum compatibility:
  1. canberra-gtk-play -i audio-test-signal (GNOME-compatible sound theme)
  2. paplay with multiple test sound paths (.oga, .ogg, .wav formats)
  3. pw-play with same test sound paths (PipeWire-native)
• 5-second timeout per command attempt
• Comprehensive tracing for debugging playback failures

i18n:

• Added sound-output.test = Test localization key (English)
• Other locales will be handled via Weblate

Visual Comparison

Before

After

Fixes #1901