Social Verify

Phase 2 "test connection": actively re-checks whether the persisted session still authenticates (services/social/social_pull.py::verify_session), rather than trusting the last-known status column the way /status does. On failure, flips the row to 'stale' via mark_stale immediately — same signal the auto-reconnect-detection paths (scheduled sync/heartbeat auth failures) write — so the frontend can render "Reconnect needed" right away instead of waiting for the next background pass.