Govern actor & payment grammar; tighten purchase and ship semantics

[GsCommand]

Motivation

• Create a single, governed commercial language across authorize, checkout, purchase, ship, and verify so the repo reads as one protocol rather than a set of ad-hoc schemas.
• Make ship clearly settlement-adjacent (fulfillment tied to an upstream commercial transaction) and lift purchase to be a first-class, well-evidenced one-step contract.
• Normalize x402/payment vocabulary and actor roles repo-wide so payment requirements, session state, and final proof are consistently named and evidence flow is predictable.

Description

• Standardized actor grammar by introducing per-schema $defs for actor_identity plus role-constrained aliases (payer_actor, payee_actor, merchant_actor, provider_actor, carrier_actor, verifier_actor) and replaced loose actor refs with these role-specific refs across all v1.1.0 commercial schemas.
• Normalized payment/x402 grammar to three canonical layers: payment_requirement (pre-payment), payment_session (live session), and payment_proof (final evidence), and aligned request/receipt fields and reference enums to use these names consistently.
• Reworked purchase into a deliberate one-step contract by adding itemized items, amount_breakdown, payment_input (accepting requirement/session/proof refs), normalized receipt statuses to captured/failed/pending, and requiring payment_proof on captured receipts.
• Tightened ship semantics by making fulfillment_ref a typed fulfillment artifact, requiring an upstream commercial_ref (must be checkout or purchase), adding payer linkage, and strengthening evidence rules so tracking_url is required when tracking_number is present, active states require carrier+tracking, and delivered requires delivered_at and delivery_proof_ref.
• Aligned authorize, checkout, and verify to the same actor/payment grammar (e.g., authorize emits payment_requirement_ref / authorization payment_proof, checkout and purchase require payment_proof on capture, verify accepts payment_proof and fulfillment targets).
• Updated examples, README.md, SPEC.md, POLICY.md, manifest.json, and checksums.txt to document and reflect the new grammar and to teach the unified model.

Testing

• Ran npm run validate to compile schemas and validate the current v1.1.0 line, and it completed successfully.
• Ran npm run validate:examples to validate all current-line examples against the updated schemas, and it completed successfully.
• Regenerated release integrity data with npm run generate:checksums and updated checksums.txt, and the checksums generation succeeded.

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Codex Task