feat: [ENG-2697] add curate-judgement sub-skill, harden curate guide

Add a post-curate self-review sub-skill and substantially strengthen the
curate authoring guide so saved topics are standalone explainers, not
changelogs.

- New src/server/templates/skill/curate-judgement.md: post-write
  self-review. After `brv curate` reports done, judge the stored,
  rendered topic against curate.md's Quality Bar with a hard cap of one
  enhancement pass (references the rubric instead of restating it to
  avoid drift).
- Register curate-judgement.md in SKILL_FILE_NAMES
  (skill-connector-config.ts) and reference it from SKILL.md (detail
  file list + command reference).
- curate.md: document the JSON envelope contract ({html, meta}
  replaces bare HTML on --response), add the four-dimension Quality
  Bar, decision-flow diagram, rationalizations/red-flags tables, a
  richer worked example exercising all dimensions, and a pre-send
  self-check; expand Required Preservation and Common Mistakes.
- Add unit coverage asserting curate-judgement.md installs as a lean
  self-review guide that points at the Quality Bar, `brv read`, and the
  one-pass --overwrite cap.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>