- Raised similarity_threshold from 0.90 to 0.95 in get_screen_type() to eliminate
POST_DETAIL false-positives caused by embedding saturation.
- Implemented purge_stale_screens() with 24h TTL to remove layout drift.
- Added collection size cap (200 points) to store_screen() with automatic wipe
when saturated to clear overfitting bias.
- Triggered purge_stale_screens() on ScreenIdentity initialization.
TDD: 3 new tests for threshold defaults and purge method integrity.