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.

pnpm-lock.yaml

@@ -2303,6 +2303,9 @@ importers:
       '@deepseek-ai/dsh-agent-spine-demo':
         specifier: workspace:^
         version: link:../agent-spine-demo
+      '@deepseek-ai/dsh-command-feedback':
+        specifier: workspace:^
+        version: link:../../feedback/command-feedback
       '@deepseek-ai/dsh-command-goal':
         specifier: workspace:^
         version: link:../../goal/command-goal
@@ -2358,6 +2361,33 @@ importers:
         specifier: ^3.17.0
         version: 3.18.0
 
+  packages/feedback/command-feedback:
+    devDependencies:
+      '@cordisjs/plugin-include':
+        specifier: workspace:^
+        version: link:../../../vendor/include
+      '@cordisjs/plugin-loader':
+        specifier: workspace:^
+        version: link:../../../vendor/loader
+      '@deepseek-ai/dsh-agent':
+        specifier: workspace:^
+        version: link:../../core/agent
+      '@deepseek-ai/dsh-commands':
+        specifier: workspace:^
+        version: link:../../ui/commands
+      '@deepseek-ai/dsh-invariants':
+        specifier: workspace:^
+        version: link:../../support/invariants
+      '@deepseek-ai/dsh-llm':
+        specifier: workspace:^
+        version: link:../../llm/llm
+      '@deepseek-ai/dsh-session':
+        specifier: workspace:^
+        version: link:../../core/session
+      cordis:
+        specifier: ^4.0.0-rc.7
+        version: 4.0.0-rc.7(@cordisjs/plugin-include@vendor+include)(@cordisjs/plugin-loader@vendor+loader)
+
   packages/fs/fs:
     devDependencies:
       '@deepseek-ai/dsh-brand':