Add sync status and last updated timestamp for GitHub data

**Is your feature request related to a problem? Please describe.**
GitHub data such as commits and issues is currently synced in the background for projects and chapters in Nest, but there is no visibility into when the last successful sync occurred or whether a sync completed fully.

With the introduction of contribution heatmaps and analytics, this lack of transparency makes it difficult for users and maintainers to assess the reliability of the displayed data. When contributions appear incomplete or outdated, there is no clear way to determine whether this is due to stale data, a partial sync, or an actual lack of activity.

**Describe the solution you'd like**
Expose basic metadata related to GitHub data synchronization, including:
- Timestamp of the last successful sync
- Status of the most recent sync (e.g. success, partial, failed)

This information could be exposed via the backend/API and optionally surfaced in the UI to help users and maintainers better understand the freshness and reliability of contribution data.

**Are you going to work on implementing this?**
- [x] Yes
- [ ] No

**Additional context**
Improving sync visibility would enhance observability and make it easier to diagnose data synchronization issues as Nest continues to expand its analytics and contribution tracking capabilities.