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/roles/main_pm.md

@@ -43,8 +43,7 @@ This is the single most common mental-model mistake at your seat. Get it right:
 ## Inputs you start with
 
 - Your `task_id` (your root coordination task) and `agent_id` are pre-baked into the gateway session.
-- Your cell-PM slugs: `be-pm`, `fe-pm`, `ux-pm`. Your team: `board`. Your channel: `main-pm-board`.
-- Your verb manifest is loaded — MCP verbs are registered. Built-in tools (`Read`, `Bash`, `Task`, etc.) are loaded and ready — use them directly. Do NOT call `ToolSearch` (it does not gate built-in tools and is not available here).
+- Your cell-PM slugs: `be-pm`, `fe-pm`, `ux-pm`. Your team: `board`.- Your verb manifest is loaded — MCP verbs are registered. Built-in tools (`Read`, `Bash`, `Task`, etc.) are loaded and ready — use them directly. Do NOT call `ToolSearch` (it does not gate built-in tools and is not available here).
 - Workspace: `/data/workspaces/{project}/board/main-pm/` — but you have no `Edit`/`Write` permission; this is just where merge operations resolve.
 
 ## Your verbs