Adopt Ghost content projection in the CLI

[aileen]

Parent

• PRD #213 — Deliver the maintained HTML-to-Algolia extraction pipeline
• User stories covered: 14–30, 48–52

What to build

Activate the released deep fragmenter contract in the CLI for the existing posts-only batch path. Carry one validated Ghost content projection from configuration through Content API fetching, complete-batch record construction, stale-record replacement, indexing, documentation, and a verified CLI minor release.

Acceptance criteria

• The CLI accepts the approved top-level contentProjection shape and validates it before any Ghost or Algolia network request.
• Omitting projection enables the approved default fields including excerpt; explicit projection, aliases, custom ranking siblings, values, and errors match the fragmenter contract.
• The Content API request sends no fields parameter and includes tags and/or authors only when those relations are enabled.
• This slice retains posts-only enumeration, current pagination behavior, and all existing CLI flag contracts.
• The complete batch is transformed and preflighted before Algolia mutation; deterministic policy/content/size failures make no request.
• For every affected legacy slug, all previous package-managed records are replaced before the validated new set is saved so shrinking content leaves no continuation.
• Projection never changes index settings implicitly and user-owned search/retrieval/facet/snippet/ranking settings remain untouched.
• Process-level acceptance uses the offline Ghost replay and external requester replacement to prove configuration, request ordering, projection, replacement, no-partial-validation, and stable outcomes.
• A scoped CLI minor release is published and verified with notes covering defaults, optional fields, aliases, display-only excerpt, size/errors, migration guidance, compatible fragmenter floor, and rollback.

Blocked by

• #220 — Release the deep fragmenter record policy