feat(voyage)!: rename type discriminators across validators + fixtures [skip-docs]

- brief-validator: BRIEF_TYPE_VALUES ['ultrabrief','ultrareview'] -> ['trekbrief','trekreview'] + dependent branches
- research-validator: 'ultraresearch-brief' -> 'trekresearch-brief'
- review-validator: 'ultrareview' -> 'trekreview'
- 3 templates frontmatter type:
- 4 synthetic fixtures: ultraplan-synthetic/ultrareview-synthetic -> trek* (frontmatter only; bodies untouched, Jaccard floor preserved)
- 2 trekreview fixtures: type: trekreview
- 6 validator-test fixtures + asserts
- agents/review-coordinator.md frontmatter example

Atomic: validator + fixtures committed together — partial state would cause vacuous
test passes or hard validator rejection.

Part of voyage-rebrand session 2 (W3.3 / Step 5).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

plugins/ultraplan-local/tests/validators/review-validator.test.mjs

@@ -3,7 +3,7 @@ import { strict as assert } from 'node:assert';
 import { validateReviewContent } from '../../lib/validators/review-validator.mjs';
 
 const GOOD_REVIEW = `---
-type: ultrareview
+type: trekreview
 review_version: "1.0"
 created: 2026-05-01
 task: "Add JWT auth"
@@ -41,7 +41,7 @@ test('validateReview — happy path', () => {
 });
 
 test('validateReview — wrong type rejected (REVIEW_WRONG_TYPE)', () => {
-  const t = GOOD_REVIEW.replace('type: ultrareview', 'type: ultrabrief');
+  const t = GOOD_REVIEW.replace('type: trekreview', 'type: trekbrief');
   const r = validateReviewContent(t);
   assert.equal(r.valid, false);
   assert.ok(r.errors.find(e => e.code === 'REVIEW_WRONG_TYPE'));