fix: forward glTF load options from triggers

[ICOM725]

Description

Trigger currently drops six glTF options before calling level.load(). Add scale, rightHanded, lights, lightIntensityScale, castGroundShadow and shadowGroundY to its forwarding list and document them.

This uses the explicit-list option from the issue, keeping unknown-setting handling unchanged. The regression tests exercise both direct loading and the fade transition through the real level-loading boundary, including false/zero values and the transition-owned async flag.

Type of change

• Bug fix
• New feature
• Documentation update
• Performance improvement
• Refactoring (no functional changes)

Checklist

• I have read the Contributing Guide
• My code follows the existing code style (pnpm lint passes)
• I have tested my changes locally (pnpm test passes)
• I have added tests that cover my changes (if applicable)
• The build succeeds (pnpm build)

Targeted verification: pnpm exec vitest run --config packages/melonjs/vitest.config.ts trigger passes (27 tests). The new forwarding assertions failed before the fix. pnpm lint, pnpm build and git diff --check pass.

The full browser suite did not complete on Windows: two Chromium Headless Shell runs stopped with unrelated module-import/iframe errors, and a separate run using installed Chrome stalled in WebGPU specs and was stopped. The full-suite checkbox is intentionally unchecked.

Related issues

Fixes #1649.