- Add abstract get_post_metrics() method to BasePublisher
- Implement get_post_metrics() in XPublisher using Twitter API v2
- Returns: likes, comments, shares, retweets, quotes, impressions
- Implement get_post_metrics() in ThreadsPublisher using Meta Graph API
- Implement get_post_metrics() in FacebookPublisher with insights
- Implement get_post_metrics() in InstagramPublisher with insights
This enables the fetch_post_metrics task to collect engagement data
from all platforms, populating the analytics dashboard.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>