Add parent dependency guard to _set_status_direct so dragging
a task to the ready column is rejected (409) when its parents
are not all done. Previously the guard only existed in
recompute_ready, allowing direct status writes via the
dashboard API to bypass the dependency engine.
Root cause: after reclaiming stale workers, both T3 and T4
were set to ready via dashboard status writes in quick
succession, causing the writer to be spawned while the analyst
was blocked — upstream work wasn't done yet.
d2c6eceed9