Fix extractReceiptVerb to read canonical receipt.verb with x402 fallback

[GsCommand]

Motivation

• A unit test expected extractReceiptVerb to read the canonical receipt.verb field but the implementation only inspected legacy receipt.x402.verb, causing CI failures.
• The change keeps legacy x402 behavior as a fallback while making the canonical path authoritative per the Commons v1.1.0 contract.
• Running the test cycle also surfaced minor TypeScript typing and naming issues that prevented a clean typecheck/build.

Description

• Updated extractReceiptVerb to delegate to the existing getReceiptVerb so the function returns receipt.verb first and falls back to receipt.x402.verb if needed (src/index.ts).
• Introduced the ReceiptProtocolMetadata type and fixed related type/generic usages and naming (receiptIdPresent, signerId) to resolve TypeScript errors (src/index.ts).
• Adjusted the unit-test fixture to include the canonical verb field so the test extractReceiptVerb reads canonical verb field validates the intended behavior (scripts/unit-tests.mjs).

Testing

• Ran npm run typecheck and it completed successfully with no type errors.
• Ran npm run build and the build artifacts were produced successfully.
• Ran npm run test:unit and all unit tests passed (44 passed, 0 failed).

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Codex Task