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/cordis.yml

@@ -3,12 +3,15 @@
 # log. The bin loads the gitignored root `.env` before this config. This tree has
 # no stdout logger or HMR because stdout carries ACP JSON-RPC.
 
-# The DeepSeek adapter.
+# The DeepSeek adapter. Shipped default: full thinking at max effort on every
+# request (wire-only defaults; they never enter the request header).
 - id: llm-deepseek
   name: '@deepseek-ai/dsh-llm-deepseek'
   config:
     apiKey: !!js process.env.DEEPSEEK_API_KEY
     baseURL: !!js process.env.DEEPSEEK_BASE_URL
+    thinking: enabled
+    reasoningEffort: max
     models:
       - id: deepseek-v4-flash
         contextWindow: 256000
@@ -51,7 +54,7 @@
   name: '@deepseek-ai/dsh-acp-demo'
   config:
     provider: deepseek
-    model: deepseek-v4-flash
+    model: deepseek-v4-pro
     persistenceRoot: !!js process.env.DSH_SNAPSHOT_SESSIONS_ROOT ?? './.sessions'
     persistenceCompression: !!js "process.env.DSH_SNAPSHOT === undefined ? 'zstd' : 'none'"
     workspaceContext: