feat: Add WizardAdapter for mounting on CLI

[razor-x]

Summary

The wizard needs two things it cannot decide for itself: the developer's Seam login, and somewhere to keep what it learns about a project. Both belong to whoever mounts it — the Seam CLI owns the login and owns where files go.

This states the shape of that answer and accepts it, and does nothing else. Split out of #7 so that seamapi/cli#614 can be built and released against it without waiting on the change that puts it to use.

The contract

export interface WizardAuth {
  endpoint: string
  apiKey: string | null
  workspaceId: string | null
}

export interface StorageAdapter {
  get: (key: string) => Promise[unknown]
  set: (key: string, value: unknown) => Promise[void]
}

export interface WizardAdapter {
  getAuth: () => Promise[WizardAuth]
  config: StorageAdapter
  state: StorageAdapter
}

await wizard({ argv, commandName: 'seam wizard', adapter })

The wizard picks the keys, the adapter picks the files. Values are plain JSON and hold no secrets.

apiKey is a workspace API key or null: it is the only credential the wizard uses, and the only kind a project's SEAM_API_KEY may be, so a personal access token is never passed at all.

Given no adapter, an in-memory one is used: every step works and nothing outlives the run.

Nothing reads it yet

Deliberately additive. Behaviour is unchanged: .seam/onboarding.json is still written, and an adapter passed in is accepted, its auth loaded once, and otherwise unused until #7 lands. So this can be released on its own, and the CLI can depend on it, before anything about the wizard's storage moves.

Changed

• New lib/adapter.ts — the interfaces, the in-memory default, and the run's adapter.
• lib/wizard.ts — an adapter option, installed before the run and asked for its auth once. --help and --version ask it nothing.
• lib/index.ts — exports the three types. Nothing else is added to the package surface.

78 tests, 16 of them new: the in-memory default, replacing the adapter, the auth being asked for exactly once, and it being forgotten when the adapter changes.