feat: Google Contacts sync integration (beyond email contacts)

[baderdean]

Summary

Implement Google Contacts synchronization to allow importing and syncing contacts beyond just email-based contacts. This extends the current Google integration to cover the full Google Contacts API.

Tasks

• Design architecture: data flow, sync direction, conflict resolution
• Define error handling strategy (rate limits, partial sync, token expiry)
• Define test coverage plan
• Implement Google Contacts API integration
• Implement sync logic (initial sync + incremental updates)
• Add UI for Google Contacts sync settings/status

Context

Design session started 2026-03-04. Architecture, data flow, and error handling were being discussed but design was not finalized or approved.

Acceptance Criteria

• Users can connect their Google Contacts account
• Contacts sync bidirectionally (or as designed)
• Error handling covers rate limits, token expiry, partial failures
• Sync status is visible in the UI
• Tests cover happy path and error scenarios