AND-245: show bundled Harness version and update action

[yaojin3616]

Summary

• show both the DSH Desktop version and the actually bundled Harness package version in About
• add a Check for Updates action to About and reuse the existing signed desktop update flow
• use the same About implementation from the Windows titlebar and native macOS app menu
• cover installed-package lookup, manifest fallback, localized copy, and menu wiring

Verification

• npm run typecheck
• npm test (27 files, 168 tests)
• npm run build

Closes AND-245
Closes #104