docs(pm-dispatch): name the main-red anchor as the fourth cross-lane channel

SKILL.md line 175, in place: the closed list of channels through which a seat
may work across a domain gains the main-red anchor beside the cross-domain
exception path, the claiming seat's follow-through surface and the unowned
blocker. Without it the seeing seat files the anchor and then stops at the
own-lane-only claim line, which is the gap the ruling ordered away; the
contract review measured this clause as the cheapest carrier. SKILL.md stays
at 319 lines, the line at 117 bytes; 红线 line 34 untouched.

Claude-Session: https://claude.ai/code/session_01LqKsGyMNFwwnbF5FTAqyPn
Co-authored-by: Claude <noreply@anthropic.com>

Author: os-warren

.claude/skills/pm-dispatch/SKILL.md

@@ -172,7 +172,7 @@ PM 的工作是循环:选卡 → 认领 → 派发 → 收集 → 复核 → 报
 - 跨域例外路径:拆不动的跨域单 PR 由分诊席指定一个车道 PM 认领,认领评论申报文件面。
 - 派发前在飞检查:读 `pm:dispatched` 卡认领评论申报的文件面,本地求交、不另发查询。
 - 跨域例外路径的范围加上该单文件面触及各域的在飞单;相交 ⇒ 排该 PR 之后串行或让行。
-- 跨域相交只经三条越界通道:跨域例外路径、认领席跟到底的越界面、接手无主阻塞项。
+- 越界只四通道:跨域例外路径、认领席跟到底的越界面、接手无主阻塞项、main-red 锚卡。
 - 合并队列是共享串行资源:车道买到的是并行编写,不是并行落地。
 - 谁发现 flake 谁修或立单,⛔ 不绕行。