Validate fixture metadata and escape report cells

[rogerchappel]

Summary

• validate optional fixture metadata as an object with string id, title, and notes fields and a string-array tags field
• preserve documented defaults for missing metadata while reporting the exact invalid meta.json path
• escape pipes and normalize newlines across fixture IDs, tags, and notes in Markdown report tables
• document the accepted metadata contract and validation behavior

Commits

• 3583926 fix: validate fixture metadata shapes
• bd69577 fix: escape markdown report cells
• a577472 docs: define fixture metadata contract

Verification

• npm ci
• npm run release:check (31 tests; syntax check; build; smoke; packed-package smoke; release contract)
• git diff --check origin/main...HEAD
• verified every commit author and committer is exactly Roger Chappel <miscanalysis@gmail.com>

[rogerchappel]

Automated merge note

Triage class: auto-merge

Summary: Validates optional fixture metadata and safely renders user-controlled Markdown report cells.

Checks run: CI test completed SUCCESS; diff reviewed; author and committer verified as Roger Chappel.

Rebased/CI-repaired: No.

Verified head SHA: a577472507274dfa679604b2763aca4c5d9504c6.