feat(gateway): root-owned acceptance criteria via declare_coverage (#357)

The coverage gates had no vocabulary for criteria only the root itself
can satisfy (the supersede PR from feature/main_pm/*, closing the
contributor's PR): once a Main PM declared coverage for the legitimate
cell criteria, the idle gate demanded a cell for the impossible ones
too, so they got pushed into a cell task and the cell PM (correctly)
escalated. declare_coverage now accepts the PM's own task: self-declared
criteria count as claimed for the idle gate and satisfied for the
roll-up (the roll-up actor is their owner by construction), surface as
claimed_by=root in the briefing, and both PM prompts say to never hand
a cell a criterion it cannot satisfy inside its own cell.

Co-authored-by: Renn F <rennf93@users.noreply.github.com>

docs/rag/lifecycle/intent-verbs.md

@@ -49,7 +49,7 @@ Cell PM merges the PR (leaf into the cell branch, or the gated cell→root PR in
 
 ## declare_coverage
 
-Stamp parent acceptance criteria onto an existing child's parent_ac_refs after the fact — for a replacement child whose delegate omitted covers_parent_criteria. No status change; the verb body owns ownership + criterion validation.
+Stamp parent acceptance criteria onto an existing child's parent_ac_refs after the fact — for a replacement child whose delegate omitted covers_parent_criteria. Or, targeting your OWN root/coordination task, declare criteria as root-owned (only your own machinery satisfies them — never push these into a cell). No status change; the verb body owns ownership + criterion validation.
 
 **Allowed roles:** cell_pm, main_pm