feat(users): per-user library assignment + themed confirm modal (#222)

Adds Navidrome library assignment to the User Management settings
panel: GET /api/library + PUT /api/user/{id}/library wired through
new Rust commands. UserForm gets a checkbox picker (hidden for
admins, who auto-receive all libraries server-side) with inline
validation. User rows compacted to a single clickable line with
hover highlight; native confirm() replaced by a portal-based
ConfirmModal (theme-aware, ESC/Enter, vertically centered).

Co-authored-by: Psychotoxical <dev@psysonic.app>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/locales/es.ts

@@ -476,6 +476,12 @@ export const esTranslation = {
     userMgmtPassword: 'Contraseña',
     userMgmtPasswordEditHint: 'Introduce una nueva contraseña para actualizarla.',
     userMgmtRoleAdmin: 'Admin',
+    userMgmtLibraries: 'Bibliotecas',
+    userMgmtLibrariesAdminHint: 'Los usuarios admin tienen acceso automáticamente a todas las bibliotecas.',
+    userMgmtLibrariesEmpty: 'No hay bibliotecas disponibles en este servidor.',
+    userMgmtLibrariesValidation: 'Selecciona al menos una biblioteca.',
+    userMgmtLibrariesUpdateError: 'Usuario guardado, pero la asignación de bibliotecas falló',
+    userMgmtNoLibraries: 'Sin bibliotecas asignadas',
     userMgmtSave: 'Guardar',
     userMgmtCancel: 'Cancelar',
     userMgmtDelete: 'Eliminar',