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/zh.ts

@@ -468,6 +468,12 @@ export const zhTranslation = {
     userMgmtPassword: '密码',
     userMgmtPasswordEditHint: '输入新密码以更新。',
     userMgmtRoleAdmin: '管理员',
+    userMgmtLibraries: '音乐库',
+    userMgmtLibrariesAdminHint: '管理员用户自动拥有所有音乐库的访问权限。',
+    userMgmtLibrariesEmpty: '此服务器上没有可用的音乐库。',
+    userMgmtLibrariesValidation: '请至少选择一个音乐库。',
+    userMgmtLibrariesUpdateError: '用户已保存，但音乐库分配失败',
+    userMgmtNoLibraries: '未分配音乐库',
     userMgmtSave: '保存',
     userMgmtCancel: '取消',
     userMgmtDelete: '删除',