feat(sdk): headless PromptPort + create/config headless plan

Add HeadlessPromptPort (fail-loud non-interactive PromptPort), thread
prefilled feature values through FeatureConfigurator, and let CreateWizard
and ConfigWorkflow accept a headless feature plan that skips the interactive
tree/suggests prompts. Per-file 100% coverage on all changed files.

packages/sdk/helper/src/index.ts

@@ -43,3 +43,4 @@ export {
 } from './questions/question.ts'
 export type { Question } from './questions/question.ts'
 export { ClackPromptPort } from './questions/clack-prompt-port.ts'
+export { HeadlessPromptError, HeadlessPromptPort } from './questions/headless-prompt-port.ts'