refactor(cli): unify the arg grammar — one program, --config flag, real web subcommand

Drop the bare `dsh <config>` positional in favor of a `--config <path>` flag.
Without a root positional, `web` can be a real Commander subcommand in one
program instead of the reserved-first-token dispatch to a second parser, so
`dsh --help` lists every mode natively (no hand-pasted command text) and the
second parser + reserved-token machinery are gone.

Grammar:
  dsh                       TUI (shipped tree + ~/.dsh overlay)
  dsh --config <path>       TUI, alternate tree (demos/tests only)
  dsh --resume <id>         TUI, resume a session
  dsh -p "task"             headless one-shot
  dsh web [--host --port --dev]

`dsh` is the product front door with no positional; `--config` exists only so
demo:cordis, demo:code-mode, and the keyless PTY smokes can point the shipped
bin at an example tree. Those three sites and the /resume re-exec argv move to
`--config <path>`. The `-p` + `--config`/`--resume` mode-mixing guard and the
cordis.yml-owns-host/port-default fix are preserved.

Agent Note + Chinese pair, README, tui.ts docs updated. All 13 PTY smokes
(including code-mode via --config and the exec-replace resume handoff) green.

scripts/demo-code-mode.mjs

@@ -7,7 +7,7 @@ import { spawn } from 'node:child_process'
 
 // Each UI's node invocation matches its base demo script plus the overlay config.
 const UIS = new Map([
-  ['tui', ['--import', 'tsx', 'apps/cli/src/bin.ts', 'examples/tui-agent/code-mode.cordis.yml']],
+  ['tui', ['--import', 'tsx', 'apps/cli/src/bin.ts', '--config', 'examples/tui-agent/code-mode.cordis.yml']],
   ['acp', ['--import', 'tsx', 'packages/examples/acp-demo/src/bin.ts', '--config', 'examples/acp-agent/code-mode.cordis.yml']],
 ])