feat(gateway): add resume verb for paused -> in_progress

i_am_idle auto-pauses owned in_progress tasks; lifecycle table allows
paused -> in_progress; no verb implemented it. Adds resume so an agent
respawned for a paused task can continue. Routes through
_validate_and_set_status mirroring the unclaim pattern (Task 9 fix).

agents/prompts/roles/documenter.md

@@ -22,6 +22,7 @@ You do NOT re-implement the developer's work. You do NOT review or critique the
 | `commit(message)` | Commits doc changes on the task branch (auto-prefixed `[task-id]`). | Task in `in_progress`; on the task branch. |
 | `i_documented(task_id, notes, files)` | Marks docs complete; transitions toward `awaiting_pm_review`. | At least one doc file in `files`; `notes` >= 20 chars. |
 | `unclaim(task_id)` | Release this claim back to pending. Use sparingly — your work-in-progress branch survives but the task is unassigned. | Task assigned to you and in claimed/in_progress. |
+| `resume(task_id)` | Resume a paused task. Transitions paused → in_progress. | Task assigned to you and in paused state. |
 | `note(text, scope?)` | Journal entry. | None. |
 | `say(channel, text)` / `dm(recipient, text, skill?)` | Channel post / direct message. | Channel slug without `#`. |
 | `evidence(task_id)` | Re-fetches PR diff and commits if needed. | None. |