feat(audio): add output port selection

[wongcallum]

Description

Adds a button to each audio output device in the control center which opens an output port selection modal. This allows users to switch from e.g. speakers to headphones without having to open pavucontrol.

I decided to add a button cuz that's how KDE Plasma does it. Happy to switch to a dropdown if preferred.

Quickshell.Services.Pipewire doesn't expose an interface to switch ports, so I used pactl in a similar way to the existing Bluetooth codec selector, using Proc.runCommand. If pactl is missing or an error happens, the button doesn't appear, so there is no need to warn about that.

This PR only handles output sinks, and only adds the selector to the control center and not the audio settings window. I'd like to open separate PRs for these to keep this one manageable. They should be fairly easy.

Type of change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that changes existing behavior)
• Refactor / internal cleanup
• Documentation
• Other

Related issues

Closes #330

Screenshots / video

output-port-selection.mp4

Checklist

• My code follows the conventions in CONTRIBUTING.md
• I have tested my changes locally
• New user-facing strings are wrapped in I18n.tr() with translator context, reusing existing terms where possible
• Go changes: ran make fmt, added/updated tests, make test passes, and go mod tidy is clean (N/A)
• QML changes: ran make lint-qml with no new warnings
• I have opened a corresponding pull request in dlx-docs to document any new behaviors: https://github.com/AvengeMedia/DankLinux-Docs