Extend the en/zh localization to the two screens reached from the home
app bar (the "全都用 + 多语言" ask):
- settings: title, theme-mode segments (System/Light/Dark), seed-color
description, color-picker + clear-data dialogs.
- search: hint, error, empty/no-results states, Notes/Documents section
headers, page label.
New ARB keys regenerated; l10n_test now asserts the new keys resolve in
both English and Chinese.
flutter analyze: 0 issues. l10n_test: 3/3.
Akiba So
a7d71e7cfd