[codex] use native-dom test environment

[Dunqing]

Summary

• Replace the direct happy-dom dev dependency with the published vitest-environment-native-dom package.
• Switch Vitest from environment: "happy-dom" to environment: "native-dom".
• Regenerate the lockfile so happy-dom is no longer resolved or installed.

Why

The native-dom environment now supports the app's DOM test surface without the local environment wrapper, and local benchmarks show it is faster than happy-dom for this suite.

Validation

• vp install --frozen-lockfile
• vp check
• vp test run - 25 files / 203 tests passed
• vp why happy-dom - no output

Benchmark Notes

Recent local wall-clock benchmark:

• vp test run: native-dom mean 1.445s
• vp test run --environment happy-dom: happy-dom mean 1.675s
• native-dom was about 1.16x faster

Memory was effectively neutral in local max-RSS sampling: native-dom averaged 541.8 MiB and happy-dom averaged 547.3 MiB.