Add ratchet for reviewed Markdown documents

[stef-k]

Reviewed oversized Markdown documents currently repeat REVIEW on every scan. Add a separate source-controlled document-size ratchet: an accepted 845-line document passes unchanged or smaller, while growth beyond its allowance returns REVIEW. New paths use ordinary thresholds, and section findings remain independent.

• Add explicit create/update commands and a strict Markdown baseline schema. Updates only lower or prune existing allowances; normal analysis never writes them.
• Share filesystem safety with the LOC workflow and retain baseline context in human/full JSON output.
• Update README, CLI help, affected guidance across /docs, skill instructions, Markdown policy, and changelog. Preserve historical research evidence.
• Keep section ratchets out of scope because stable section identity needs separate design.

Validation: 333 tests pass against a fresh wheel installation; compileall and git diff checks pass. Independent code/documentation review found no blockers. Code Guard covered all 18 changed files: accepted runner LOC, parser length, and analysis orchestration length/complexity REVIEW findings; no FAIL or INCOMPLETE results.

Closes #128.