fix: export/import — отмена пользователем не показывает error toast

Bug: при отмене save-dialog или open-dialog DataCard показывал тост
«Не удалось сохранить» / «Файл не подошёл». Но cancel — это не ошибка.

Расширил IPC возврат: { ok, canceled, path?, error? }. UI теперь
различает: ok → success toast, !ok && canceled → молча, !ok && !canceled
→ error toast.

+9 тестов на validateSettingsPatch для voicePromptsEnabled,
meetingAutoPause, lastSeenVersion (semver-regex / null-сброс /
malformed). Итого 159 → 168 тестов.

Settings → About теперь показывает текущую версию приложения
(раньше была только кнопка «Что нового»). Загружается через
IPC.getAppVersion при mount.

src/main/validate.test.ts

@@ -266,6 +266,65 @@ describe('validateSettingsPatch', () => {
     expect(validateSettingsPatch({ snoozeMinutes: -5 })).toBeNull()
   })
 
+  it('accepts voicePromptsEnabled boolean', () => {
+    expect(validateSettingsPatch({ voicePromptsEnabled: true })).toEqual({
+      voicePromptsEnabled: true
+    })
+    expect(validateSettingsPatch({ voicePromptsEnabled: false })).toEqual({
+      voicePromptsEnabled: false
+    })
+  })
+
+  it('rejects non-boolean voicePromptsEnabled in patch', () => {
+    expect(validateSettingsPatch({ voicePromptsEnabled: 'yes' })).toBeNull()
+    expect(validateSettingsPatch({ voicePromptsEnabled: 1 })).toBeNull()
+  })
+
+  it('accepts meetingAutoPause boolean', () => {
+    expect(validateSettingsPatch({ meetingAutoPause: true })).toEqual({
+      meetingAutoPause: true
+    })
+  })
+
+  it('rejects non-boolean meetingAutoPause', () => {
+    expect(validateSettingsPatch({ meetingAutoPause: 'yes' })).toBeNull()
+  })
+
+  describe('lastSeenVersion', () => {
+    it('accepts valid semver', () => {
+      const r = validateSettingsPatch({ lastSeenVersion: '0.5.7' })
+      expect(r?.lastSeenVersion).toBe('0.5.7')
+      expect(validateSettingsPatch({ lastSeenVersion: '10.20.30' })).toEqual({
+        lastSeenVersion: '10.20.30'
+      })
+    })
+
+    it('accepts pre-release suffix', () => {
+      const r = validateSettingsPatch({ lastSeenVersion: '0.5.7-beta.1' })
+      expect(r?.lastSeenVersion).toBe('0.5.7-beta.1')
+    })
+
+    it('treats null/undefined as reset to undefined', () => {
+      const r1 = validateSettingsPatch({ lastSeenVersion: null })
+      expect(r1).toEqual({ lastSeenVersion: undefined })
+      const r2 = validateSettingsPatch({ lastSeenVersion: undefined })
+      // 'lastSeenVersion' is `in raw` even if undefined — both treated reset.
+      expect(r2).toEqual({ lastSeenVersion: undefined })
+    })
+
+    it('rejects malformed strings', () => {
+      expect(validateSettingsPatch({ lastSeenVersion: '0.5' })).toBeNull()
+      expect(validateSettingsPatch({ lastSeenVersion: 'v0.5.7' })).toBeNull()
+      expect(validateSettingsPatch({ lastSeenVersion: 'beta' })).toBeNull()
+      expect(validateSettingsPatch({ lastSeenVersion: '' })).toBeNull()
+    })
+
+    it('rejects non-strings', () => {
+      expect(validateSettingsPatch({ lastSeenVersion: 42 })).toBeNull()
+      expect(validateSettingsPatch({ lastSeenVersion: ['1', '0', '0'] })).toBeNull()
+    })
+  })
+
   describe('quietHours subobject', () => {
     const baseQh = {
       enabled: true,