fix: custom designs fall back to Card on newer Omarchy

[TerrifiedBug]

On current Omarchy dev builds, every custom design in ~/.config/omarchy/lock-designs shows up as Card, both on the lock screen and in previews. Nothing in the logs.

It comes from Omarchy's new Quickshell load patch (their Qt 6.12 Color workaround). It gives .pragma library files two instances, so the Designs.USER list that Service.qml fills in is empty when LockHost.qml reads it, and resolve() falls back to the default. Reported over there: omacom/omarchy-pkgs#978

This stops keeping that list in Designs.js. Service holds it as userDesigns (also on the explorer facade), the lookup functions take it as an argument, and LockHost, Explorer and Editor pass it through. Works the same with or without the patch.

extras/test-service-api.py, extras/qml-syntax-check.sh and tests/*.cjs all pass. On my machine my custom design shows up again in omarchy-shell lock previewDesign.