Fix v1.1.0 commercial schema blockers: verify $ref, purchase duplicates, requester docs, and duplicate-key guard

[GsCommand]

Motivation

• Eliminate release-blocking schema errors that break strict AJV compilation and create ambiguous JSON artifacts.
• Restore intended commercial semantics for purchase receipts (strict x402 proof) and verify flows (explicit verifier typing).
• Make duplicate-key regressions easier to detect in CI by adding a small pre-parse guard.

Description

• Replace the broken inlined verifier actor in schemas/v1.1.0/commercial/verify/verify.receipt.schema.json with a reference to the existing #/$defs/verifier_actor, preserving the role = verifier constraint.
• Remove duplicate $defs.settlement and duplicate payment_proof keys from schemas/v1.1.0/commercial/purchase/purchase.receipt.schema.json and keep the stricter x402_proof shape as the active payment_proof mapping.
• Clarify requester semantics by updating schemas/v1.1.0/commercial/verify/verify.request.schema.json description and the two main normative docs (README.md, SPEC.md) to state that requester is a verify-specific initiator field reusing the general actor identity rather than adding a new governed actor role.
• Add a lightweight duplicate-object-key detector (assertNoDuplicateObjectKeys) to scripts/validate-all.mjs and scripts/validate-examples.mjs so JSON sources fail fast before JSON.parse can hide duplicate keys, and regenerate checksums.txt to reflect the schema edits.

Testing

• Ran npm run validate and it passed (schema tree, AJV strict compile, index/manifest/layout checks all OK).
• Ran npm run validate:examples and it passed (all verb example groups validated as expected).
• Confirmed verify.receipt compiles under strict AJV with a focused ajv.compile check and it succeeded.
• Ran the duplicate-key source check against schemas/v1.1.0/commercial/purchase/purchase.receipt.schema.json and verified the file is valid JSON with no duplicate object keys.
• Regenerated checksums.txt and re-ran integrity validation; the integrity check passed.

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Codex Task