refactor(ui): fold the stdio UI helper into the stdio app

The readline UI lives inside @deepseek-ai/dsh-stdio-agent as the
in-package stdio-chat module; the packages/support/ui-stdio package is
gone. The app's front-door cluster always includes this UI and nothing
else composes it, so the boundary bought manifest/tsconfig/module-graph/
README/publint surface for a helper that is not independently
swappable — and a product app no longer depends on a support package
documented as not-product-surface.

createStdioChat, the StdioRuntime test seam, and both unit suites moved
verbatim (imports rewired to the module path); the named
name/inject/Config/apply export shape stays, being the contract the
app's ctx.plugin mount consumes. Coverage stays per-file 100%; the
built-bin smoke under plain node and both keyless Loader-path smokes
prove the published artifact and the demos end-to-end.

Implements docs/rfc/implemented/simplification/2026-07-04-fold-stdio-ui-helper.md
(moved from proposed/ and amended to the shipped shape).

pnpm-lock.yaml

@@ -774,25 +774,6 @@ importers:
         specifier: ^4.0.0-rc.6
         version: 4.0.0-rc.6(@cordisjs/plugin-include@1.0.4)(@cordisjs/plugin-loader@1.0.0-rc.4)
 
-  packages/support/ui-stdio:
-    dependencies:
-      schemastery:
-        specifier: ^3.18.0
-        version: 3.18.0
-    devDependencies:
-      '@deepseek-ai/dsh-agent':
-        specifier: workspace:^
-        version: link:../../core/agent
-      '@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.6
-        version: 4.0.0-rc.6(@cordisjs/plugin-include@1.0.4)(@cordisjs/plugin-loader@1.0.0-rc.4)
-
   packages/todo/tool-todo:
     devDependencies:
       '@deepseek-ai/dsh-agent':
@@ -922,9 +903,6 @@ importers:
       '@deepseek-ai/dsh-session-persistence-jsonl':
         specifier: workspace:^
         version: link:../../session-persistence/session-persistence-jsonl
-      '@deepseek-ai/dsh-ui-stdio':
-        specifier: workspace:^
-        version: link:../../support/ui-stdio
       cordis:
         specifier: ^4.0.0-rc.6
         version: 4.0.0-rc.6(@cordisjs/plugin-include@vendor+include)(@cordisjs/plugin-loader@vendor+loader)