resolveFolderIcon
resolveFolderIcon(key) turns a stored FOLDER_ICONS
key into its MDI icon component, or null for an unset or unknown key —
the caller then falls back to its default glyph.
<component
:is="resolveFolderIcon(folder.customIcon) ?? Safe"
:size="18"
:fill-color="resolveFolderColor(folder.customColor, currentTheme())" />
The null-for-unknown contract is what keeps older frontends
forward-compatible with keys written by a newer catalog: nothing throws,
the default glyph renders, and the stored value survives untouched.