feat(player): Windows HDMI audio bitstream passthrough

[umarjamilpc]

Summary

Adds an opt-in Windows-only HDMI audio passthrough setting so Dolby/DTS bitstreams (including Atmos / DTS:X where the receiver supports them) can be sent unchanged over the Windows default HDMI endpoint via WASAPI exclusive + libmpv audio-spdif. Default remains decoded PCM for speakers/headphones.

Rebased onto current Dev (0ce22855). One conflict resolved in PlayerEngine.desktop.kt (kept new initialPositionMs / initialPositionRequestKey keys and added windowsHdmiPassthroughEnabled).

PR type

• Reproducible bug fix
• UI glitch/bug fix
• Behavior bug/regression fix
• Small maintenance only, with no UI or behavior change
• Docs accuracy fix
• Translation/localization only
• Approved larger or directional change

Why

Windows desktop currently always decodes to PCM, so AV receivers (e.g. Denon) see stereo/PCM instead of Dolby Atmos / DTS:X even when other Windows players bitstream correctly on the same HDMI path.

Feature request: #250 (open, labeled enhancement; filed for maintainer review/approval per CONTRIBUTING).

Desktop scope

• Windows x64: settings toggle + native WASAPI exclusive / audio-spdif path
• Shared settings storage/repository + Playback Settings UI (Windows-gated)
• macOS: JNI create signature parity only (unused bool)
• Android/iOS: expect/actual stubs only (no behavior)

Issue or approval

Feature request: #250

UI / behavior impact

• No UI change
• No behavior change
• UI changed only to fix a documented glitch/bug
• Behavior changed only to fix a documented bug/regression
• UI change has explicit maintainer approval
• Behavior change has explicit maintainer approval

Policy check

• I have read and understood CONTRIBUTING.md.
• This PR is small, focused, and limited to one problem.
• This PR is scoped to the desktop app, desktop packaging, desktop documentation, or shared code required for desktop behavior.
• This PR is not cosmetic-only.
• Any UI change fixes a linked glitch/bug and includes visual proof, or this PR has no UI change.
• Any behavior change fixes a linked bug/regression or has explicit approval, or this PR has no behavior change.
• This PR does not bundle unrelated refactors, cleanups, formatting, or drive-by changes.
• This PR does not add dependencies, architecture changes, migrations, or product-direction changes without explicit approval.
• I listed the testing performed below.

Note: #250 is the linked feature request. Maintainer approval on that issue is still pending; opening this PR so the author can review the ready implementation against current Dev.

Scope boundaries

Intentionally not included:

• In-app HDMI device picker
• TorrServer / installer / login config changes
• Non-Windows platforms enabling passthrough

Testing

• Manual Windows x64 testing of the HDMI passthrough path against a Denon HDMI receiver (bitstream engages when toggle on; PCM when off) on the earlier implementation branch
• Rebased onto latest Dev with conflict resolution only in PlayerEngine.desktop.kt; no app rebuild in this update pass
• Verified native JNI signature parity (Windows + macOS create) and settings expect/actual stubs after rebase

Screenshots / Video

UI addition is a Windows-only Playback Settings switch (not a glitch fix). Happy to attach a settings screenshot on request.

Breaking changes

None when the toggle is left off (default). When enabled, software volume/speed are skipped while bitstreaming (receiver controls volume).

Linked issues

#250

[KhooLy]

Looks good overall, but volume/speed are currently disabled whenever the setting is enabled, even if mpv falls back to decoded PCM. Please only disable them while passthrough is actually active, and rebase/test this against current Dev.