fix(sdk): list create <source> and headless flags in usage help

dsh-sdk's usage template predates the create command and create-sdk's
predates --config/--config-json/--json, so --help hid both surfaces the
README already documents. Pin each with a help-output assertion.

packages/sdk/create-sdk/src/templates/assets/usage.txt.tpl

@@ -9,3 +9,6 @@ Options:
   --interface <acp|stdio|embed>
   --pm <npm|pnpm|yarn>
   --install / --no-install
+  --config <path>
+  --config-json <json>
+  --json