feat(bundle): the web and one-shot apps own their own flags

dsh-web-app owns --host/--port/--dev/--workspace-root/--trusted-host and
its --help in a web-startup row; the rows it configures wait for the
webStartup service, and the client-plugin HMR receiver now ships disabled
so --dev is a row toggle rather than a runtime insert (the Loader cannot
resolve a row inserted from inside a mounting plugin).

dsh-headless owns the task positional and rejects a missing task as its own
usage error. Its runner ships disabled, not merely waiting: the schema
requires the task, and a row's config is validated when its fiber is
created, before the startup row can supply one. A composition has exactly
one command-line owner, so the patch disables the web startup row and this
one provides webStartup too, leaving the web rows on their composed
one-shot values.

The keyless web scaffold provides the same three values with no arguments,
which is what an embedding host with no command line does.

packages/bundle/headless/README.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write packages/bundle/headless/README.md
-README.md: f8b76b77f2beb22f501a49f0fc4cf5cd72223765
-README.zh.md: aae8ab5bea663b8909de942f72615f5ef9b16c84
+README.md: 45c87f0c85cbb68ad0366ea5f2c86e55fc307309
+README.zh.md: 22322692450fa85a87e9faf903abee0d38968f91