feat(feedback): add a /feedback command recorded through the command plane

Register a global `/feedback` command so a user can record a remark about the
session without spending a model turn. `/feedback <text>` acknowledges; empty
or whitespace-only input returns a usage error.

The plugin appends no session event of its own. `dsh-commands` already writes
a `command/run` / `command/done` pair for every dispatched command, carrying
the verbatim text and the settled outcome, and both records are log-only and
non-surface. The feedback is therefore durably in the session log and invisible
to the model without this package touching the log format.

Text is never parsed, so `/feedback /plan felt slow` records that literal
content. Nothing consumes the records; capture is deliberately inert.

New group `packages/feedback/` — no existing group owns feedback capture. Its
row raises the packages/README.md word ceiling by 10, which had no headroom;
one redundant sentence there was removed to offset most of the cost.

packages/feedback/README.zh.md

@@ -0,0 +1,11 @@
+# feedback/：记录的人类反馈
+
+[English](README.md) | 中文
+
+feedback 家族让人类记录对会话的评价，但不据此采取任何动作。反馈属于持久的会话日志内容，与模型对话以及后续可能读取它的任何策略相互独立。
+
+| 包 | 职责 | ctx 键 |
+|---|---|---|
+| `command-feedback/` | 面向用户的 `/feedback` 命令，通过命令平面完成记录 | 无 |
+
+被记录的评价仅写入日志：它绝不会进入模型 surface 或派生历史，随附插件也不会消费它。未来的消费方从会话日志中读取命令记录，而不是改变它们的采集方式。