Cascade an operator snooze from a governor to its governed tasks

[tildesrc]

Snoozing a task muted that one row only, so a snoozed governor's ensemble kept demanding attention — bright rows, still counted in active agents N/M — even though the operator had said "not today" to the work they belong to.

TaskService.set_snooze now writes the same snoozed_until onto every non-terminal task governed (transitively) by the snoozed one, mirroring the existing cascade-drop:

• Terminal descendants are skipped (a finished task demands no attention to mute), but the walk descends through them, so a completed child doesn't shield a live grandchild from its governor's snooze.
• Clearing cascades the same way — un-snoozing a governor un-snoozes its ensemble. A child's own longer snooze is overwritten by its governor's.
• Nothing cascades upward: e on a governed task mutes that task alone (this fork has no attention/piercing field).
• An unchanged value is skipped, so a repeated snooze causes no updated_at/change-feed churn, and a seen set keeps a governance cycle (set_governor doesn't reject one) from looping.
• Tasks created under an already-snoozed governor don't inherit it; snoozing the governor again re-cascades.
• The service still stores the string verbatim and never reads a clock — whether a deadline is active stays a dashboard display decision.

The dashboard needs no change: each child now carries the fact on its own record, so the existing _snooze_label / dimming / counter / refresh-timer paths mute it.

Plan: the task's plan.md artifact.