fix(pipewire): mute route-less virtual sources

[kvnloo]

Summary

Mute route-less virtual audio sources (EasyEffects virtual microphones) by continuing past mixer-api to the existing SPA PROP_mute node write. Hardware sources that already have a DeviceRoute stay mixer-api-only.

Audio/Source/Virtual is collapsed to Audio/Source after #3846, so panel mute currently writes mixer-api, sets optimistic swMute for the icon, and returns before SPA mute. That stops capture on routed hardware mics but leaves EasyEffects filter-graph capture live.

Motivation

#4226 — muting the selected EasyEffects virtual microphone flips the muted icon while capture still passes. Hardware "Kreo Sonic Analog Stereo" mutes correctly. Virtual recognition (#3846) listed these sources; it did not make mute stop capture.

Type of Change

• Bug fix
• New feature
• Breaking change
• Refactoring
• Build / packaging

Related Issue

Closes #4226

Testing

• clang-format 22.1.8 --dry-run --Werror on src/pipewire/pipewire_service.cpp: exit 0
• git diff --check: exit 0
• Standalone control-flow contract virtual_source_mute_test.cpp:
  • baseline (-DBASELINE): exit 1 — route-less virtual source must receive a direct SPA node mute
  • candidate 1736d19f75c37e177e18d2b2f9d3f6897842ef13: exit 0 — PASS
  • cases: route-less source gets SPA mute; routed hardware source stays mixer-only; program stream retains SPA mute; device source without mixer retains SPA mute
• Full Meson/Ninja suite was not run; this host has no EasyEffects capture graph. The change is the early-return gate in PipeWireService::setNodeMuted only.

Manual Coverage

• Tested on Niri
• Tested on Hyprland
• Tested on Sway
• Tested on another compositor:
• Tested with different bar positions and density settings
• Tested at different interface scaling values
• Tested with multiple monitors

No live EasyEffects session was available on the verification host.

Screenshots / Videos

N/A — mute control-flow, no UI layout change.

Checklist

• This PR is ready for review, or it is marked as Draft.
• I read and followed the relevant guidance in CONTRIBUTING.md.
• I ran just format with clang-format v22+ installed, or this PR has no code changes.
• I ran the relevant build or test commands, or explained why they were not run.
• I self-reviewed the changes.
• I checked for new warnings or errors.
• I updated user-facing documentation in docs/user/ when this PR changes documented behavior or configuration, or this PR does not require documentation changes.
• I added or updated assets/translations/en.json, or this PR adds no new user-facing strings.
• I did not edit non-English translation files unless this PR is explicitly for translation tooling, an import/export sync, or a maintainer-requested locale change.
• I used the existing canonical names for config keys, IPC names, paths, and identifiers.

Additional Notes

Candidate SHA 1736d19f75c37e177e18d2b2f9d3f6897842ef13 on baseline a1a0e0ffc841af1f77901bc7ebc81c104ed8d56e. Does not implement #3274 (visual mute desync). Does not change default-device selection.

[Krak8]

Thanks for the mic fix :)