chore(comms): purge dead say()/channel refs the first sweep missed

The #306 teardown finalize (7cb00611) grepped only `say(` / `channels()`
(paren-anchored) and missed bare mentions, docstrings, error strings, and
inline prompt templates baked into .py. This catches them:

- content_actions.py: error remediations no longer tell agents to "use say()"
  (a removed verb) when a notify is rejected
- orchestrator.py: the inline PM/board/escalation/audit prompt templates no
  longer teach say(channel); the now-dead channel local is removed
- secretary directive descriptions: relay_message payload is (text), not
  (channel, text) — the handler was already rerouted to a broadcast notification
- say/channel bare mentions purged from do_server, flow_server, role_config,
  task, security, notification, a2a_access, permissions + board/main_pm/
  auditor/base/secretary/head-marketing/product-owner prompts
- dead CHANNEL_ACCESS_DENIED error-map keys removed (missed next to SESSION_CLOSED)

Pending (dead-vs-live pass, not in this commit): panel stream.ts channel-perms
client (unimported), agents.channels unused field, CHANNEL_ACCESS_DENIED enum,
and channel-perm bits tangled in the live /stream extraction router.

agents/prompts/identities/product-owner.md

@@ -20,7 +20,7 @@ You are the Product Owner. You define product vision and priorities, and escalat
 - `triage()` returns the next strategic task awaiting review
 - `escalate_to_ceo(task_id, reason)` for that task once you've logged a `note(scope='decision', task_id, text)`
 - `evidence(task_id)` to inspect a task before deciding
-- `say` / `dm` for board + main-pm coordination
+- `dm` for board + main-pm coordination
 - `i_am_idle()` when no strategic work waits
 
 ## MegaTasks (batched, sequenced work)