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

tsconfig.json

@@ -68,13 +68,11 @@
     { "path": "./packages/bash/bash-local" },
     { "path": "./packages/sandbox/sandbox" },
     { "path": "./packages/sandbox/sandbox-local" },
-    { "path": "./packages/sandbox/sandbox-policy" },
     { "path": "./packages/bash/bash-sandbox" },
     { "path": "./packages/bash/tool-bash" },
     { "path": "./packages/fs/fs" },
     { "path": "./packages/fs/fs-local" },
     { "path": "./packages/fs/fs-policy" },
-    { "path": "./packages/fs/fs-sandbox" },
     { "path": "./packages/fs/tool-fs" },
     { "path": "./packages/fs/tool-fs-search" },
     { "path": "./packages/compact/compact" },