[codex] Add WebGL renderer benchmark comparison

[meekmachine]

Summary

Adds a WebGL renderer benchmark page that uses the same shared procedural Loom3 benchmark harness added in #163.

This is stacked on #163 intentionally, so this PR's diff is only the comparison layer:

• npm run benchmark:webgl
• examples/webgl-benchmark/index.html
• examples/webgl-benchmark/main.js
• README update documenting both renderer benchmark commands

The result shape matches the WebGPU benchmark exactly and writes to the browser console plus window.__loom3BenchmarkResult.

How to run

npm run benchmark:webgl

Open the printed local URL and inspect the browser console.

Validation

• npm test passed: 28 files, 179 tests.
• npm run build passed.
• npm run typecheck passed.
• Browser smoke via Chrome remote debugging passed against http://localhost:4173/examples/webgl-benchmark/.

Smoke result excerpt:

{
  "renderer": "WebGLRenderer",
  "threeRevision": "170",
  "rendererFlags": {
    "isWebGPURenderer": false,
    "isWebGLRenderer": true,
    "backend": null
  },
  "setup": {
    "hairRegistrationCount": 1,
    "morphMeshCount": 2
  },
  "submitMs": {
    "avg": 0.2,
    "p95": 0.3,
    "p99": 0.4
  },
  "approximateFpsFromRaf": 71.978
}

Notes

Because this PR targets #163's branch, checking out this top branch gives both benchmark commands for side-by-side browser-console comparison.

[meekmachine]

PR backlog triage — DRAFT_KEEP (stacked on #163)