cleanup(config): remove literal credential compatibility residue

Adapter schemas now carry only credential references, but the Models join, onboarding readiness, shipped overlays, SDK scaffolding, fixtures, and active decision prose still treated a redacted literal apiKey as a supported compatibility state. That residue made an unsupported field look contractual and pinned Schemastery silent-dropping as behavior.

Delete those branches and examples, and let compositions and scaffolds use adapter-owned reference and environment resolution. Do not add a tombstone validator or change generic unknown-key behavior: literal adapter credentials have no migration contract to preserve.

packages/sdk/create-sdk/tests/create.spec.ts

@@ -381,7 +381,7 @@ describe('CreateWizard and scaffolder', () => {
     }).run()
     await scaffoldProject(resolved.directory, resolved.request)
     expect(await readFile(join(resolved.directory, '.env'), 'utf8')).toBe(
-      '# Required before start; an empty value makes provider startup fail.\nDEEPSEEK_API_KEY=\n',
+      '# Required before the first model request.\nDEEPSEEK_API_KEY=\n',
     )
     expect(port.requests).toContain('Keep the API key empty and fill .env later?')
   })