Add post-v1 shared-rule drift guard

[Shaelz]

Adds deterministic CI validation for the shared canonical/bootstrap rule blocks.

Adds explicit shared-rule markers and aligns the bootstrap embedded shared-rule snapshot to canonical wording. Future bootstrap-generated project-local skill content now receives synchronized shared-rule content; installer behavior is unchanged.

Freezes the former v1 release plan as docs/releases/v1.0-validation-record.md while leaving docs/V1_RELEASE_PLAN.md as a compatibility pointer.

Validation performed:

• final shared-rule drift check pass;
• controlled prose, duplicate-marker, structural-indentation, heading-hierarchy, and orphan-end-marker failure proofs;
• ASCII punctuation check pass;
• staged diff whitespace check pass.

This PR contains post-v1 maintenance hardening only. No merge is requested as part of this task.

[Shaelz]

Follow-up correction: the first shared-rule-drift workflow run failed at startup because the pinned actions/checkout SHA was accidentally truncated to 39 characters. Commit ea1c54c replaced it with the verified full-length actions/checkout v6.0.2 SHA. The rerun completed successfully: https://github.com/Shaelz/codebase-orient-skill/actions/runs/26362866265. No repository Actions/settings change was required.