Populate admin ingestion status with run history and freshness signals

## Parent PRD

#1

## What to build

Turn the admin ingestion-status skeleton into a useful operator surface by showing recent sync runs, latest success/failure state, and top-level freshness signals for Google Sheets and YouTube. This slice should deliver an end-to-end internal status page that answers whether ingestion is healthy right now.

## Acceptance criteria

- [ ] Admins can view recent ingestion run history and top-level freshness indicators on the status page.
- [ ] The status surface distinguishes successful and failed runs and exposes newest-seen source timestamps that are available today.
- [ ] Tests cover the status read model and admin-only access behavior.

## Blocked by

- Blocked by #2

## User stories addressed

Reference by number from the parent PRD:

- User story 5
- User story 6
- User story 7
- User story 8
- User story 11
- User story 29
- User story 30