Retire the readline front door and the repl-agent example

Delete packages/ui/stdio and examples/repl-agent; rename stdio-demo to
@deepseek-ai/dsh-tui-demo (TUI-only, refuses pipes before Loader boot).
tui-agent owns the coding composition inline; echo-agent and the CI demo
smoke move to the one-shot cli-demo bin, which gains -p/--prompt. The
UI-independent with-key e2es move verbatim to tui-agent. SDK wizard's
'stdio' interface becomes 'tui'. PTY testing stays confined to TUI
surfaces; all other subprocess tests ride pipes.

See .agents/notes/implemented/simplification/2026-07-20-retire-readline-front-door.md

examples/acp-agent/code-mode-workspace-context.cordis.yml

@@ -1,5 +1,5 @@
-# Code Mode workspace-context snapshot recording overlay. The default filesystem
-# tools trigger nested instruction discovery after a read.
+# Code Mode workspace-context snapshot recording overlay. The scenario needs
+# filesystem tools to trigger nested instruction discovery after a read.
 - id: base
   name: '@cordisjs/plugin-include'
   config:
@@ -21,5 +21,13 @@
 
             Verify your work by running the code or tests. Keep answers brief and factual.
       - insert:
+          - id: fs-local
+            name: '@deepseek-ai/dsh-fs-local'
+            config:
+              cwd: !!js process.cwd()
+          - id: fs-policy
+            name: '@deepseek-ai/dsh-fs-policy'
+          - id: tool-fs
+            name: '@deepseek-ai/dsh-tool-fs'
           - id: code-runtime
             name: '@deepseek-ai/dsh-code-runtime-worker'