feat(web): seat the plan control on conversation.input.plan over the projection

Rewrite ui-plan as a pure browser surface plugin. The control occupies the
composer's named plan seat (declared empty by ui-conversation); reads render
the host-computed plan projection through the standard-kit useProjection
(absent key = capability absence, hides the control), writes execute /plan
or /plan off through command.execute. The node half becomes the empty
roster apply: plan behavior (command, policy, projection unit) is owned by
dsh-plan-mode, already composed on the web roster with its policy in
cordis.yml. The superseded RPC-backed setPlanMode face, the WEB_PLAN_SECTION
duplicate, and the node-plugin spec are removed; the roster row moves from
the retired CLIENT_PACKAGES table to the cordis.yml dshClient roster.

pnpm-lock.yaml

@@ -1095,7 +1095,10 @@ importers:
         version: 18.3.1
 
   packages/client/ui-plan:
-    dependencies:
+    devDependencies:
+      '@deepseek-ai/dsh-client-connection':
+        specifier: workspace:^
+        version: link:../connection
       '@deepseek-ai/dsh-client-runtime':
         specifier: workspace:^
         version: link:../runtime
@@ -1105,37 +1108,24 @@ importers:
       '@deepseek-ai/dsh-client-ui-slots':
         specifier: workspace:^
         version: link:../ui-slots
-      '@deepseek-ai/dsh-plan-mode':
-        specifier: workspace:^
-        version: link:../../plan/plan-mode
-      react:
-        specifier: ^18.2.0
-        version: 18.3.1
-    devDependencies:
-      '@deepseek-ai/dsh-client-connection':
-        specifier: workspace:^
-        version: link:../connection
       '@deepseek-ai/dsh-client-web-react':
         specifier: workspace:^
         version: link:../web-react
       '@deepseek-ai/dsh-invariants':
         specifier: workspace:^
         version: link:../../support/invariants
-      '@deepseek-ai/dsh-system-prompt':
+      '@deepseek-ai/dsh-plan-mode':
         specifier: workspace:^
-        version: link:../../core/system-prompt
-      '@deepseek-ai/dsh-tools':
-        specifier: workspace:^
-        version: link:../../core/tools
-      '@deepseek-ai/dsh-user-interaction':
-        specifier: workspace:^
-        version: link:../../ui/user-interaction
+        version: link:../../plan/plan-mode
       '@types/react':
         specifier: ~18.3.1
         version: 18.3.31
       cordis:
         specifier: ^4.0.0-rc.7
         version: 4.0.0-rc.7(@cordisjs/plugin-include@1.0.4)(@cordisjs/plugin-loader@1.0.0-rc.5)
+      react:
+        specifier: ^18.2.0
+        version: 18.3.1
 
   packages/client/ui-primitives:
     dependencies: