feat(ui): add dedicated TUI package

Move the interactive pi-tui front door into @deepseek-ai/dsh-tui while keeping @deepseek-ai/dsh-stdio line-oriented for pipes. Select the terminal package in the demo app, preserve logger ownership, and cover the production Loader composition with a PTY smoke test.

knip.json

@@ -1,7 +1,7 @@
 {
   "$schema": "https://unpkg.com/knip@5/schema.json",
   "exclude": ["duplicates"],
-  "ignoreBinaries": ["bwrap", "sandbox-exec"],
+  "ignoreBinaries": ["bwrap", "python3", "sandbox-exec"],
   "ignoreWorkspaces": ["vendor/*", "python/sdk-runtime"],
   "workspaces": {
     ".": {