feat(presets): add per-preset output device association

[dennislemennace]

What this does

Adds an opt-in "Remember output device" checkbox to the Presets panel. When checked at save time, the currently selected output device is stored alongside the preset. When that preset is later loaded — from the panel or the tray icon — the app automatically switches to that device, making profile switching a single action.

Default behaviour is completely unchanged: presets saved without the checkbox never affect the output device.

Implementation details

Storage — a new preset_devices.json sidecar file managed by PresetManager, structured as a JSON object mapping preset name → {deviceId, useDefault}. This mirrors the existing preset_rules.json pattern and deliberately keeps device names out of the portable .conf preset files, since they are machine-specific.

Apply path — applyPresetDevice() sets AppConfig::AudioOutputDevice + AppConfig::AudioOutputUseDefault, which triggers a live device switch via PipewireAudioService::onAppConfigUpdated — the same path SettingsFragment uses when the user picks a device manually.

Import safety — the association is applied only when loading a managed preset from the presets directory. Files opened via Load custom audio.conf (MainWindow::loadExternalFile(), which also flows through loadFromPath()) never switch the device, even if the imported file's base name happens to collide with a saved preset.

Feedback-loop guard — the existing onOutputDeviceChanged rule system loads presets in response to device changes. A _suppressDeviceApply flag prevents the loaded preset from firing another device change in that code path.

Rename/delete sync — PresetManager::rename() and remove() keep _presetDevices in sync so stale entries don't accumulate.

PulseAudio — the new checkbox is hidden under #ifdef USE_PULSEAUDIO alongside the existing Rules button, since the PulseAudio device-switching path is stubbed (PulsePipelineManager hardcodes use_default_sink = true).

Incidental fix

PresetFragment::onAddClicked() previously cleared the name field with ui->presetName->text() = "";. Because QLineEdit::text() returns a QString by value, this assigned to a throwaway temporary and the field was never actually cleared after saving. Replaced with ui->presetName->clear().

Files changed

• src/data/PresetManager.h — new map, path helper, load/save/set/clear/has/apply declarations
• src/data/PresetManager.cpp — full implementation + hooks in loadFromPath (scoped to managed presets), rename, remove, onOutputDeviceChanged
• src/interface/fragment/PresetFragment.ui — rememberDevice QCheckBox (added to tab order)
• src/interface/fragment/PresetFragment.cpp — checkbox wired to save/reflect state; hidden on PulseAudio; incidental clear() fix

[dennislemennace]

Hi, I am new to github and this is my first PR using LLM. This is a feature which is super convenient for my use case, which is having different profile presets for each device. This allows the output device to be saved with the preset if the checkbox is enabled. I have built and tested on Bazzite and seems to work well. Please consider approving this, and let me know if I can improve this PR in anyway! Thanks for the great software :)