refactor(cli): parse dsh argv through one Commander adapter

Replace the dsh CLI's three hand-rolled parsing idioms (raw argv[0]/includes
dispatch in bin.ts, per-mode node:util parseArgs in headless.ts/web.ts, and the
bespoke parseResumeArg scanner in dsh-app-boot) with a single Commander adapter
in apps/cli/src/args.ts. parseDshArgs resolves argv into a discriminated
DshInvocation union; bin.ts switches on the mode and dynamic-imports the chosen
module, which now consumes already-parsed values.

- web is a real subcommand; --host uses choices and --port an argParser range
  check, moving validation into the parser.
- --resume rejects empty and repeated forms; --prompt rejects empty; a config
  positional after --prompt and a root flag placed before web fail loud.
- adds --help/--version; removes parseResumeArg from dsh-app-boot.
- new apps/cli/tests/args.spec.ts (apps/*/tests added to vitest include,
  apps/cli/tests to tsconfig.host.json); the tui-agent keyless PTY smoke covers
  bin.ts dispatch end to end unchanged.

apps/cli/README.md

@@ -2,6 +2,8 @@
 
 The `dsh` command-line entry follows the `apps/` assembly tier: `apps/*` are product assemblies over `packages/*` libraries. Plain `dsh [config.yml]` boots the interactive TUI coding agent, `dsh -p "task"` runs one headless turn, and `dsh web` serves the browser UI.
 
+Argv is parsed once through a [Commander](https://github.com/tj/commander.js) adapter ([`src/args.ts`](src/args.ts)) that resolves the invocation into a single mode; `src/bin.ts` switches on that mode and dynamic-imports only the chosen mode's module. `dsh --help` and `dsh web --help` render usage, `dsh --version` prints this app's version, and an unknown option or an invalid `--host`/`--port`/`--resume` value fails loud (stderr, exit 1) instead of misrouting.
+
 The TUI surface:
 
 - boots the shipped default config (`examples/tui-agent/cordis.yml`) or an explicit config argument, through [`dsh-app-boot`](../../packages/ui/app-boot/README.md);