Docs-only: require semver-pinned x402 entry format in POLICY/README/SPEC

[GsCommand]

Motivation

• Make protocol documentation and examples explicit about semver-pinned x402 entry routes so on-chain TXT bindings and resolver logic target full v<major>.<minor>.<patch> routes.
• Limit the follow-up to docs-only changes to address review feedback without touching schema, artifacts, or checksums.

Description

• Updated POLICY.md to require the entry pattern x402://<ens>/<verb>/v<major>.<minor>.<patch> in the Validation Requirements section.
• Updated README.md table, examples, and ENS TXT binding snippets to use semver-pinned entry URIs and v1.0.0 sample values.
• Updated SPEC.md normative rule, explanatory text, and examples to require semver-pinned x402 routes (and note the route should align with the published card release).
• This PR is strictly docs-only and does not change schemas, agent artifacts, or checksums.txt.

Testing

• Ran npm run validate, which executes card validation, checksum verification, and type-checking, and it completed successfully.

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