[codex] deterministic rule depth pack

[PSkinnerTech]

Summary

• Adds Phase D.2 deterministic rule-depth helpers for structured-data visible-content mismatch, entity clarity gaps, and exact-preview duplicate content clusters.
• Wires the new page-level and site-level findings into the audit engine and CLI rule explanation coverage.
• Adds helper, integration, and end-to-end audit regression tests, plus validation manifest and changelog updates.

Validation

• node --test packages/cli/test/rule-depth.test.mjs packages/cli/test/rules.test.mjs packages/cli/test/cli.test.mjs packages/cli/test/rule-engine.test.mjs packages/cli/test/site-rule-engine.test.mjs packages/cli/test/audit.test.mjs passed 88/88.
• npm test passed 219/219.
• npm run validate passed with ok: true.
• git diff --check main..HEAD passed.

Notes

• Duplicate content clusters intentionally use exact normalized visibleTextPreview fingerprints for D.2, with tests guarding against same-body/different-title false positives.