Tighten release metadata validation and fix example validator

[GsCommand]

Motivation

• Remove remaining release-surface and validation ambiguity by making path semantics explicit and ensuring the example validator actually reads current-line fixtures.
• Clarify that cross-repo alignment metadata in the manifest is declarative-only and add steward succession language so governance has an explicit continuity mechanism.
• Eliminate an accidental duplicate publishConfig entry and regenerate checksums so integrity validation covers the updated artifacts.

Description

• Fix scripts/validate-examples.mjs to use the imported readdir helper so example files are discovered and validated via the shared strict JSON loader.
• Tighten scripts/validate-all.mjs to assert path_base and paths_are_repo_relative on manifest.json and schemas/v1.1.0/index.json, and to require alignment_verification === "declarative-only".
• Add path_base and paths_are_repo_relative to schemas/v1.1.0/index.json and add path_base, paths_are_repo_relative, and alignment_verification to manifest.json to remove path-framing ambiguity and record alignment mode.
• Add succession language to GOVERNANCE.md, document the declarative-only alignment claim in README.md, remove the duplicate trailing publishConfig block from package.json, and regenerate checksums.txt to cover the updated manifest and index metadata.

Testing

• Ran npm test (which runs the validate aggregate), and the full suite passed after fixes.
• Ran node scripts/validate-all.mjs and it completed successfully validating manifest, index, and schemas.
• Ran node scripts/validate-examples.mjs and it validated all current-line examples.
• Ran node scripts/generate-checksums.mjs followed by node scripts/validate-integrity.mjs and the regenerated checksums.txt validated the release integrity surface.

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Codex Task