feat(audio): add lossless HDMI passthrough

[cjohnsto-nz]

Summary

• add a minimal audio output selector and Passthrough toggle to Settings and the player audio quick menu
• pass AC-3, E-AC-3, TrueHD/Atmos, DTS, and DTS-HD through unchanged when supported by the selected device
• reattempt passthrough after output-device and mode changes by refreshing playback at the current demux position
• distinguish requested settings from observed mpv output so passthrough is only reported after audio-out-params/format becomes spdif-*
• replace the volume control with a passive dotted-speaker indicator while passthrough is active
• use a shared custom dropdown component for Settings and player controls
• add concise hover hints to the quick output selector and Passthrough toggle
• group the controls under Audio immediately after Rendering

Why

Soia currently decodes all audio through the PC mixer. This adds an explicit path for sending supported encoded streams unchanged to an HDMI receiver while keeping the normal PCM path as the default.

Runtime

This branch pins the official mpv v0.41.0-r16 release, produced after FengZeng/mpv#3 enabled and verified FFmpeg's SPDIF muxer.

The normal compact dynamic-runtime architecture is unchanged. This does not introduce a conditional runtime source, fork-specific dependency, static binary overlay, or bundled diagnostic artifact.

The PR remains draft while the rewritten branch completes CI and final review.

Product behavior

• PCM remains the default.
• Passthrough uses the selected output device and automatically uses WASAPI exclusive mode for eligible encoded tracks.
• Changing the device or toggling Passthrough back on creates a fresh SPDIF attempt.
• A zero-distance exact seek restarts the SPDIF decoder at a valid demux boundary, avoiding intermittent TrueHD parser failures after route changes.
• Failed encoded negotiation is reported instead of decoded PCM being presented as successful passthrough.
• Unsupported codecs such as FLAC, AAC, and Opus continue through decoded PCM without disabling the preference for future eligible tracks.
• Volume, mute, and speed changes are unavailable while encoded passthrough is active.
• Device identifiers remain internal; only readable descriptions are displayed.
• Existing development settings migrate to the minimal mode plus outputDevice contract.

Validation

• pnpm build
• 12 focused Rust audio tests passed
• hardware validation confirmed reliable TrueHD passthrough after startup, mode toggles, and output-device changes
• mpv release CI passed for Windows, macOS, and Linux on x64 and ARM64: https://github.com/FengZeng/mpv/actions/runs/30737604752
• pnpm setup:libs resolved and installed the official r16 Windows x64 release
• local integration built successfully with pnpm bundle:win:release

The full Rust suite currently has three unrelated upstream failures. All reproduce on upstream/main: two playlist/core state assertions and the existing Windows path-separator assertion.

[FengZeng]

@cjohnsto-nz The new release of mpv v0.41.0-r16 with spdif muxer enabled in ffmpeg is ready now

Also have two small suggestions for the Settings page:

1. Maybe rename the Audio Output section to Audio, so we have a place to add more audio related settings in the future.
2. Maybe move this section a bit higher, for example right after Rendering, since audio settings are important for many users.

[cjohnsto-nz]

@FengZeng I have addressed your feedback, and pushed a couple of additional fixes.
I am happy for this to be kept open for a few days so I can test in real world use.

[FengZeng]

There are still a few bugs on macOS. I’m also planning to redesign the Audio popup in the Playback UI, so I temporarily removed the audio passthrough settings from it