docs(pm): batch default back to 3 on the maintainer's ruling — ceiling 5 unchanged

One line in `.claude/skills/pm-dispatch/SKILL.md` 〈入口与角色〉: the
`batch:<n>` table row's default moves 2 → 3 on the maintainer's ruling
「并发2 还是太慢了，默认恢复3吧」. The maintainer ceiling 5, the write-identity
locks, `LOCK_DEPTH_HOLD` and the same-file serial rule are untouched;
`references/core-rules.md` states no batch default, so it has no mirror line.
Equal-line and byte-neutral: 812/812 lines, 73524 bytes before and after,
frame block (lines 733–754) md5 unchanged.

Claude-Session: https://claude.ai/code/session_01DAcomhvR9kKizeYgg89Vo8
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude[bot]

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

@@ -57,7 +57,7 @@ PM 的工作是循环:选卡 → 认领 → 派发 → 收集 → 复核 → 报
 | `director` | 以项目总监席身份运行(人工召唤;四职见 升级与决策 节与 `references/lanes/director.md`) | — |
 | `label:<name>` | backlog 过滤标签;`label:all` = 全部 open 未认领 | `pm:queue` |
 | `repo:<owner/name>` | 扫哪个仓的 backlog(单 issue 的落地仓看它自己的 `repo:*` 标签) | `objectstack-ai/objectstack` |
-| `batch:<n>` | 同时在飞的 dev 上限 | 默认 `2`;`n` 的维护者天花板 `5` |
+| `batch:<n>` | 同时在飞的 dev 上限 | 默认 `3`;`n` 的维护者天花板 `5` |
 | `rounds:<n>` | 跑 N 轮后停 | 队列清空为止 |
 | `mode:subagent` \| `mode:cloud` | 派发后端 | 按卡分流:S+M ⇒ `subagent`,`cloud` 只留 L/XL 等保留面 |
 | `#12 #34 …` | 显式 issue 清单,整体覆盖标签查询 | — |