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/client/ui-models/tests/readiness.spec.ts

@@ -19,7 +19,6 @@ function row(overrides: Partial<ProviderRow> = {}): ProviderRow {
     removable: false,
     apiKeyEnv: 'DEEPSEEK_API_KEY',
     credential: missingCredential,
-    literalApiKeyConfigured: false,
     ...overrides,
   }
 }
@@ -64,13 +63,6 @@ describe('deepSeekReadiness', () => {
     }))).toEqual({ kind: 'configured' })
   })
 
-  it('accepts the redacted literal-key sidecar before judging the credential domain', () => {
-    expect(deepSeekReadiness(state({
-      credentialError: 'credentials service absent',
-      rows: [row({ literalApiKeyConfigured: true, credential: undefined })],
-    }))).toEqual({ kind: 'configured' })
-  })
-
   it('turns missing capabilities and inconsistent descriptors into diagnostics', () => {
     expect(deepSeekReadiness(state({ status: 'error', error: 'settings down' }))).toEqual({
       kind: 'unavailable',