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/package.json

@@ -19,6 +19,7 @@
     "@deepseek-ai/dsh-host-runtime": "workspace:^",
     "@deepseek-ai/dsh-host-webserver": "workspace:^",
     "@deepseek-ai/dsh-paths": "workspace:^",
-    "@deepseek-ai/dsh-session": "workspace:^"
+    "@deepseek-ai/dsh-session": "workspace:^",
+    "commander": "^15.0.0"
   }
 }