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.

examples/tui-agent/tests/pty-harness.ts

@@ -192,10 +192,12 @@ export async function runTuiPtySmoke(options: TuiPtySmokeOptions): Promise<strin
     await options.prepare?.(cwd)
     const launch = resolveExampleLaunch({
       srcBin: options.binScript,
+      // `configPath` is the dsh `--config <path>` tree override; `configArgs`
+      // is the raw-args escape (e.g. `['--resume', <id>]`) for other flags.
       configArgs: options.configArgs !== undefined
         ? [...options.configArgs]
         /* v8 ignore next -- every caller passes configPath or configArgs; the fallback keeps the type total */
-        : [options.configPath ?? './cordis.yml'],
+        : options.configPath !== undefined ? ['--config', options.configPath] : [],
       tsconfigPath: options.tsconfigPath,
       env: {
         DSH_HOME: join(cwd, '.dsh'),

examples/tui-agent/tests/tui-keyless-smoke.e2e.ts

@@ -253,7 +253,7 @@ describe('dsh CLI keyless smoke (apps/cli through the same PTY)', () => {
       label: 'dsh in-place resume',
       tempDirPrefix: 'dsh-in-place-resume-',
       binScript: dshBinScript,
-      configArgs: [scriptedConfigPath],
+      configPath: scriptedConfigPath,
       prepare: seedResumeSession,
       actions: [
         { waitFor: 'scripted TUI ready.', send: '/resume\r' },
@@ -350,7 +350,7 @@ describe('dsh CLI keyless smoke (apps/cli through the same PTY)', () => {
       label: 'dsh source-path prompt',
       tempDirPrefix: 'dsh-source-path-',
       binScript: dshBinScript,
-      configArgs: [scriptedConfigPath],
+      configPath: scriptedConfigPath,
       actions: [
         ...SELECT_PRO_MODEL,
         { waitFor: 'Model selected: tui-scripted/tui-scripted-model-pro.', send: 'exercise the TUI\r' },