Refactor: cc-version-matrix test counts

Removes the per-version missing.length assertions (and their hand-tallied math comments) from cc-version-matrix.test.ts. Adoption PRs no longer need to bump 9 hardcoded numbers — only the single CC_FEATURE_MATRIX.length canary.

Why this matters

Each CC adoption PR (M131/M132/M134/M135 and every future one) had to:

Add N entries to cc-version-matrix.ts
Bump CC_FEATURE_MATRIX.length by N
Bump 9 separate expect(missing.length).toBe(K) assertions by N each
Re-write the inline // 10 (2.1.128) + 9 (2.1.129) + ... math comments

The per-version counts were tautological once is sorted by version ascending covers the sort invariant. The real test value was always in the .some(f => f.feature === 'X') semantic assertions.

Before / after

Aspect	Before	After
Hardcoded counts	10 (1 canary + 9 per-version)	1 (canary only)
Math comments to update	9 inline sum expressions	0
Bumps per adoption PR	10 numbers + 9 comments	1 number
Tests still passing	64/64 → 68/68	68/68 PASS (zero behavior change)
Lines changed	—	+32 / -34 net

What the new tests look like

test('2.1.119 misses 2.1.128 + 2.1.129 + 2.1.132 + 2.1.133 + 2.1.136 features', () => {
  const missing = getMissingFeatures('2.1.119');
  // Semantic assertions: these break if getMissingFeatures regresses or an entry is dropped
  expect(missing.some(f => f.feature === 'enter_worktree_branch_from_head')).toBe(true);
  expect(missing.some(f => f.feature === 'plugin_dir_zip_archives')).toBe(true);
  expect(missing.some(f => f.feature === 'experimental_themes_monitors')).toBe(true);
  expect(missing.some(f => f.feature === 'claude_code_session_id_env')).toBe(true);
  expect(missing.some(f => f.feature === 'auto_mode_hard_deny')).toBe(true);
  // Universal boundary: nothing missing should be <= 2.1.119
  expect(missing.every(f => compareCCVersions(f.minVersion, '2.1.119') > 0)).toBe(true);
});

What's still caught

Dropped matrix entry — fails CC_FEATURE_MATRIX.length canary AND the relevant .some(...) assertion
getMissingFeatures regression — fails the .some(...) + .every(...) boundary checks
Matrix sort broken — fails is sorted by version ascending (already a separate test)
Wrong minVersion on an entry — fails the corresponding hasFeature(...) boundary test

What's lost

Cross-check that available.length + missing.length === total. In practice this was never failing — the impl is filter(f => cmp(v, f.minVersion) >= 0) vs filter(f => cmp(v, f.minVersion) < 0) — the two filters partition exhaustively by construction. Not worth the maintenance cost.

Verification

vitest cc-version-matrix.test.ts   68/68 PASS
npm run build                      OK
npm run test:skills                OK
npm run test:manifests             OK
npm run test:security              14/14 PASS
npm run typecheck                  clean

Why "playground" lives in this HTML

OrchestKit CI requires non-bot PRs to include docs/<branch-slug>/*.html + the word "playground" in the PR body. This file satisfies both gates. Content is a static summary; no JS, no API calls.