Tribu 1.6.1

What's changed

• fix contact-synced birthdays to use stable contact IDs instead of person_name
• keep same-name contacts separate in the calendar and preserve the correct synced birthday row on rename, delete, and date updates
• show a real automatic build/version identifier in Settings > About instead of branch placeholders like vmain

Verification

• backend regression coverage for birthday identity and version resolution
• frontend regression coverage for version formatting and calendar birthday handling
• local end-to-end calendar verification for duplicate-name birthday behavior