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/tests/questions.spec.ts

@@ -450,4 +450,35 @@ describe('feature configurator', () => {
     await expect(new FeatureConfigurator(new QueuePromptPort([])).configure(new EmptyExclusive(), profile))
       .rejects.toThrow('has no default option')
   })
+
+  it('configures fully from prefilled options, values, and secrets without prompting', async () => {
+    const registry = createBuiltinRegistry(profile)
+    const port = new QueuePromptPort([])
+    const result = await new FeatureConfigurator(port).configure(
+      registry.get(featureId('provider')),
+      profile,
+      undefined,
+      ['custom'],
+      { apiKey: 'prefilled-key' },
+      { baseURL: 'https://prefilled' },
+    )
+    expect(result).toMatchObject({
+      options: ['custom'],
+      values: { baseURL: 'https://prefilled' },
+      secrets: { apiKey: 'prefilled-key' },
+    })
+    expect(port.requests).toEqual([])
+  })
+
+  it('rejects a non-string prefilled feature value', async () => {
+    const registry = createBuiltinRegistry(profile)
+    await expect(new FeatureConfigurator(new QueuePromptPort([])).configure(
+      registry.get(featureId('provider')),
+      profile,
+      undefined,
+      ['custom'],
+      { apiKey: 'k' },
+      { baseURL: 123 },
+    )).rejects.toThrow('must be a string')
+  })
 })