feat: delete the legacy 17-row eval matrix — the sliced lane is the only paid lane

Every PR paid twice: the hand-enumerated matrix (18 test files, 22.6 min,
~$21 API measured on run 33263204465) ran serialized AHEAD of the strictly
superior sliced lane via 'needs: evals' — 35.5 min wall and ~2x paid spend
for the same diff. 14 of 17 rows carried no tier:, so periodic Opus
benchmarks leaked into every PR (the e2e-plan row alone: 12/12 tests,
21.7 min, $7.28 — the wall-clock bound of ALL of CI).

Parity receipt (static, pre-deletion): the sliced lane's gate census (49
files, derived from the runner itself) strictly contains all 18 matrix test
files, plus 31 files the matrix never ran. Pure deletion — one revert
restores it. The PR comment moved into slices-report (same '## E2E Evals'
upsert marker, now sourced from slice artifacts + carrying the fail-closed
reconciliation verdict). plan-slices loses the needs edge; the dead
workflow-level EVALS_TIER env goes with it.

test/evals-workflow-matrix.test.ts (and its KNOWN_MATRIX_GAPS /
KNOWN_TIER_UNSET burn-down ratchets — retired: the sliced census makes
'every gate file runs' true by construction) is rewritten as
test/evals-workflow-wiring.test.ts: matrix stays deleted, planner/executor/
report tier + slice-count agreement, both surviving lanes on the shared
register-skills composite with its fail-fast verification loop, PR comment
survival. Expected: PR eval wall 35.5 -> ~13 min, per-PR paid spend ~halved.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/e2e-tier-alignment.test.ts

@@ -42,8 +42,8 @@ const SELF_GATE_RE = /EVALS_TIER\s*===\s*['"](gate|periodic)['"]/g;
 const HELPER_GATE_RE = /\b(?:describeE2ETier|e2eTierEnabled)\(\s*['"](gate|periodic)['"]/g;
 
 /**
- * Ratchet, not amnesty (same contract as KNOWN_MATRIX_GAPS in
- * test/evals-workflow-matrix.test.ts): skill-e2e files that are named in NO
+ * Ratchet, not amnesty (the contract KNOWN_MATRIX_GAPS pioneered before the
+ * legacy eval matrix and its test retired): skill-e2e files that are named in NO
  * touchfiles dep list because no E2E map key exists for them. Every entry
  * carries a one-line reason. Do NOT add new files here — give the test an
  * E2E map key (touchfiles + tier) and register the file in its dep list.
@@ -141,8 +141,8 @@ describe('E2E tier alignment (touchfiles declaration vs test self-gate)', () =>
     expect(misaligned).toEqual([]);
   });
 
-  // Ratchet cleanup enforcement (same contract as evals-workflow-matrix's
-  // burn-down test): a KNOWN_UNREGISTERED entry whose file was deleted, or
+  // Ratchet cleanup enforcement (same shrink-only contract as the retired
+  // matrix test's burn-down): a KNOWN_UNREGISTERED entry whose file was deleted, or
   // whose file is now named in a dep list, is stale — delete the entry so
   // the set can only shrink.
   test('KNOWN_UNREGISTERED holds only live, still-unregistered files', () => {