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.

panel/src/hooks/use-rate-limit-websocket.ts

@@ -53,7 +53,7 @@ export function useRateLimitWebSocket(
   const prevStateRef = useRef<string | null>(null);
 
   // getWebSocketUrl() already supplies the "/ws" base, so the endpoint is just
-  // the path (matching the agents/channels/notifications hooks). Passing
+  // the path (matching the agents/notifications hooks). Passing
   // "/ws/system" here produced the doubled "/ws/ws/system" URL.
   const { state, lastMessage } = useWebSocket<SystemWsMessage>(
     "/system",