Unify purchase receipt payment outcomes

[GsCommand]

Motivation

• Remove semantic drift between checkout.receipt and purchase.receipt by standardizing payment outcome vocabulary to payment-native values captured / failed / pending.
• Ensure one-step (x402) purchase receipts carry the same evidence as checkout receipts by surfacing payment_proof for successful settlements.
• Preserve minimal, targeted scope: converge purchase toward the existing checkout model without broad schema changes.

Description

• Updated purchase.receipt status enum from accepted/rejected/pending to captured/failed/pending in schemas/v1.1.0/commercial/purchase/purchase.receipt.schema.json.
• Reused checkout's x402 proof shape by adding the x402_proof $defs and a payment_proof property to purchase.receipt, and required payment_proof when top-level status is captured via conditional allOf rules.
• Kept existing reason conditional for non-settled outcomes (failed/pending) so error reasoning remains required in those cases.
• Updated examples to match the new model: examples/v1.1.0/commercial/purchase/valid/900-purchase.receipt.valid.json now uses status: "captured" and includes an x402 payment_proof, and examples/v1.1.0/commercial/purchase/invalid/900-purchase.receipt.invalid.json was adjusted to exercise the missing-proof failure path.
• Files edited: schemas/v1.1.0/commercial/purchase/purchase.receipt.schema.json, examples/v1.1.0/commercial/purchase/valid/900-purchase.receipt.valid.json, and examples/v1.1.0/commercial/purchase/invalid/900-purchase.receipt.invalid.json.

Testing

• Ran npm run validate and the full schema validation suite, which completed successfully.
• Ran npm run validate:examples and all example sets validated, including the updated purchase examples.
• Example validation confirms the valid captured receipt requires payment_proof and the invalid fixture remains invalid for the intended missing-proof case.

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Codex Task