feat: add deterministic Ghost check JSON report

[chailandau]

Why

Enterprise review systems need a deterministic Ghost JSON contract they can run in CI or a first-party review bot, then map into their existing PR comment and status workflows without Ghost owning GitHub posting identity.

What

• Adds ghost check for detector-backed ghost.check/v1 markdown checks.
• Emits ghost.check-report/v1 JSON with path/line findings for review orchestrators.
• Supports forbidden-regex and required-regex detectors over unified diff additions.
• Leaves checks without detector: in the existing agent-evaluated ghost checks lane.
• Documents the generic enterprise review integration boundary and regenerates the CLI manifest.

Validation

• pnpm build
• pnpm check
• pnpm test

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