feat(ui): 主题切换 + 语言持久化 + About 对话框

- 新增 light/dark 主题调色板与 Windows 注册表系统主题探测
- 偏好设置对话框：主题三选一 + 语言下拉(en/zh-CN/de)，即时生效
- 持久化 Language/Theme/AutoLockMinutes/MinimizeToTray 至 YAML 顶层
- 启动时按 config 中保存的语言初始化 i18n
- About 对话框展示 version/runtime/项目地址/许可证
- 全部硬编码颜色迁移到 themePalette，为深色模式做准备

internal/ui/store.go

@@ -26,6 +26,13 @@ type store struct {
 	passphrase []byte
 	encrypted  bool
 
+	// Top-level user preferences kept alongside entries so save() can
+	// roundtrip them without requiring the UI to rebuild a full Config.
+	language        string
+	theme           string
+	autoLockMinutes int
+	minimizeToTray  bool
+
 	// dirty signals a save is pending. The worker reads & resets it.
 	dirty       bool
 	snapshotFn  func() []config.Entry
@@ -37,6 +44,27 @@ type store struct {
 	onError func(error)
 }
 
+// Preferences returns the persisted top-level prefs. UI code reads these
+// after Load to seed dialog defaults.
+func (s *store) Preferences() (language, theme string, autoLockMinutes int, minimizeToTray bool) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	return s.language, s.theme, s.autoLockMinutes, s.minimizeToTray
+}
+
+// SetPreferences updates the persisted top-level prefs and schedules a
+// save. Callers pass the current value for each field — there is no
+// per-field "leave unchanged" sentinel.
+func (s *store) SetPreferences(language, theme string, autoLockMinutes int, minimizeToTray bool) {
+	s.mu.Lock()
+	s.language = language
+	s.theme = theme
+	s.autoLockMinutes = autoLockMinutes
+	s.minimizeToTray = minimizeToTray
+	s.mu.Unlock()
+	s.Push()
+}
+
 // newStore initializes a store and starts the background save worker.
 // snapshotFn is invoked whenever a save runs; it must return a freshly
 // copied entries slice (the worker holds no UI locks). onError is called
@@ -86,6 +114,10 @@ func (s *store) Load(passphrase []byte) (*config.Config, error) {
 	s.mu.Lock()
 	s.passphrase = passphrase
 	s.encrypted = cfg.Encrypted
+	s.language = cfg.Language
+	s.theme = cfg.Theme
+	s.autoLockMinutes = cfg.AutoLockMinutes
+	s.minimizeToTray = cfg.MinimizeToTray
 	s.mu.Unlock()
 	logger.WithField("entries", len(cfg.Entries)).Debug("config loaded into store")
 	return cfg, nil
@@ -148,13 +180,21 @@ func (s *store) run() {
 		s.dirty = false
 		pw := append([]byte(nil), s.passphrase...)
 		enc := s.encrypted
+		lang := s.language
+		theme := s.theme
+		autoLock := s.autoLockMinutes
+		minToTray := s.minimizeToTray
 		s.mu.Unlock()
 
 		entries := s.snapshotFn()
 		cfg := &config.Config{
-			Version:   1,
-			Encrypted: enc,
-			Entries:   entries,
+			Version:         1,
+			Language:        lang,
+			Theme:           theme,
+			AutoLockMinutes: autoLock,
+			MinimizeToTray:  minToTray,
+			Encrypted:       enc,
+			Entries:         entries,
 		}
 		if err := config.SaveYAML(cfg, s.path, pw); err != nil {
 			global.Log.WithField("func", fn).WithError(err).Error("save failed")