Bench: supersede frontend runner pin after class capture lowering

Reproduction

Pushed CI 33135419183, benchmark-comparison-harness, fails at f83c419:

V29 measured-boundary native runner changed without a matrix version bump: bench/frontend_parse.zig

#803 correctly updated the frontend class-frame/TDZ structural guards and capture-plan checksum when class lowering became available, but did not supersede the frozen representative matrix runner hash. This is an integration omission, not a measured performance regression.

Acceptance

• Add V30 inheriting the exact immutable V29 hash and repin only the changed frontend native runner. Keep all workload, timing, checksum, attribution, occupancy, provenance and publication contracts unchanged.
• Update the loader's supported version/default, future-version rejection test and current documentation. Retain mutation tests that reject stale runner pins.
• Pass the complete Home benchmark harness self-test inventory; preserve prior artifacts and do not publish any performance claim from this dirty worktree.
• Track descendant pushed CI before closing this issue and #803/#804/#805.

Completed integration (2026-08-28 UTC)

Implementation: 18cd4530. The measured local evidence above and in the linked implementation comments remains unchanged.

• Complete pushed integration: CI 33144524467 at descendant 81978f7b completed successfully: 53 jobs passed, one scheduled-only job skipped, zero failures. This supersedes earlier pending, cancelled, or failed integration reports; those earlier runs are not counted as successful gates.

Closing this implemented issue as completed. Parent-roadmap work and independently tracked follow-ups remain open; this closure does not claim those broader scopes are finished.

Landed as 18cd4530: immutable V30 inherits V29 and repins only the frontend runner. Home matrix mutation checks pass 65/65, docs-link-check resolves 308 files, and checked BunPress renders 50 pages. No engine change or Test262 flips; no public performance claim. The complete benchmark inventory and descendant pushed CI remain pending, so this issue stays open.

Current descendant integration: https://github.com/zig-utils/zig-js/actions/runs/33137549779 at f2340f27. The 18cd453 run was superseded after 16 successful jobs and no failures, not counted as complete. Local 65/65 matrix mutation checks and docs gates pass. The full 18-module Home benchmark inventory is still type-checking imported tools (sampled active compiler work); no complete-inventory success is claimed yet. Keeping this open.

The full local Home benchmark harness has now completed successfully: all 18/18 validators pass, including the 65/65 representative-matrix mutation checks. Complete log retained at /Users/chris/.cache/zig-js-parameter.jIiaXW/matrix-v30-self-tests.log. Pushed integration at https://github.com/zig-utils/zig-js/actions/runs/33137549779 remains the final gate; no benchmark performance result is inferred from these structural self-tests.