Adapt session model selection to the slash/input/session architecture

- host trio kept on the merged api-proxy: session.models (provider-grouped
  advisory directory), session.selectModel (validated provider, advisory
  model), installAgentLlmTarget threaded through create/resume/ensureSession;
  the gateway declares the llm inject it reads
- history no longer piggybacks modelTarget: the current target travels on
  session.models alone (the /model popup is the sole consumer)
- new @deepseek-ai/dsh-client-ui-model plugin: /model popupSelect over the
  wire — options load the directory (group label in the detail column,
  provider-local failures listed inline), onSelect routes selectModel;
  failures ride the popup shell's error/retry surface
- ModelSelector package, conversation.composer.control slot, and the
  Session-side modelSelection state machine are removed: model selection
  belongs to the /model popup; the named conversation.input.model seat
  stays empty until a control-seat entry is designed for it

apps/cli/cordis.yml

@@ -300,6 +300,10 @@
 - id: ui-subagent
   name: '@deepseek-ai/dsh-client-ui-subagent'
 
+# Model selection: the /model popupSelect over session.models / selectModel.
+- id: ui-model
+  name: '@deepseek-ai/dsh-client-ui-model'
+
 - id: ui-question
   name: '@deepseek-ai/dsh-client-ui-question'
 

apps/cli/package.json

@@ -29,6 +29,7 @@
     "@deepseek-ai/dsh-client-ui-command": "workspace:^",
     "@deepseek-ai/dsh-client-ui-conversation": "workspace:^",
     "@deepseek-ai/dsh-client-ui-layout": "workspace:^",
+    "@deepseek-ai/dsh-client-ui-model": "workspace:^",
     "@deepseek-ai/dsh-client-ui-models": "workspace:^",
     "@deepseek-ai/dsh-client-ui-question": "workspace:^",
     "@deepseek-ai/dsh-client-ui-settings": "workspace:^",