fix: avoid duplicate ambient lights

[besmpl]

Summary

• remove the second direct-child ambient-light collection pass
• collect every light type through the existing visible scene traversal
• prevent direct ambient nodes from occupying two frame-uniform slots
• make ambient lights obey the same nested visibility rules as other lights

Why

buildFrameUniforms already finds AmbientLight through lightFromNode during TraverseVisible. It then scanned direct children again with collectAmbientLights, so a normal scene containing one ambient and one directional light reported three lights and applied the ambient contribution twice. The second scan also included hidden ambient nodes.

Verification

• baseline regression: one ambient plus one directional produced LightCount == 3
• baseline regression: hidden direct ambient nodes were still collected
• direct ambient and directional sources are now counted once each
• visible nested ambient sources remain supported
• hidden nodes and hidden subtrees are skipped
• max-light truncation remains unchanged
• go test ./...
• go test -race ./...
• go build ./...
• go vet ./...
• gofmt and git diff --check

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[kolkov]

Code reviewed: correct fix — removes redundant collectAmbientLights, traversal already handles ambient via lightWithUniform interface. 3 tests cover dedup, nested groups, hidden nodes. LGTM.