test(benchmarks): consolidate product verification

[thejustinwalsh]

Summary

• remove implementation-shaped benchmark unit tests that duplicated production modules, UI markup, renderer internals, and closed milestone probes
• retain deterministic low-level raster references, benchmark contracts, public product targets, package integration tests, and browser-level product verification
• reduce this layer by 4,249 net lines without changing production renderer code

Verification

• complete root pnpm test passed
• benchmark Vitest: 24 files / 113 tests
• all 19 deterministic headless Chromium product and conformance scenarios passed
• packed consumer produced the authenticated 172,156-byte artifact

This is PR 1 of 3 in the workflow-cleanup checkpoint.