audio: add dynamic playback and capture route selection

[Srikanth Muppandam (smuppand)]

Add runtime audio-route discovery without hard-coded card, PCM, sink, or source names.

Changes

• Automatically select playback routes in this order:
  • Speakers
  • Headphones/headset
• Automatically select capture routes in this order:
  • Built-in microphone
  • Headset microphone
• Support explicit speaker, headset, mic, and headset-mic overrides.
• Validate explicit routes against discovered runtime capabilities.
• Discover routes through PipeWire, PulseAudio, ALSA, and UCM.
• Apply the same routing model to:
  • AudioPlayback
  • AudioRecord
  • AudioLoopback
• Improve direct ALSA fallback and diagnostics.
• Accept valid RIFF chunks following WAV audio data.
• Preserve portability across Yocto, Debian, Ubuntu, and other supported distributions.

Result handling

• Explicitly requested unavailable routes report an actionable FAIL.
• Automatic discovery reports SKIP when no usable physical route is available.
• Functional playback, recording, and loopback failures remain FAIL.

Fixes #454