fix: fix layer-0 ByLayer inheritance for INSERT material remapping (issue #219)

[mlightcad]

Summary

• Fixes layer-0 block entities so ByLayer traits inherit INSERT layer values during render and later layer edits.
• Introduces typed material metadata with per-trait ByLayer flags to make remapping and layer updates deterministic.
• Adds unit and e2e regression coverage (with fixture + snapshot) for INSERT/layer-0 color inheritance behavior.

Why

• Some layer-0 block paths could lose explicit isByLayerColor while still being logically ByLayer, causing incorrect inherited color behavior.
• A single isByLayer flag was too coarse for correctly applying inherited updates across color, linetype, lineweight, and transparency.
• Issue layer color change not applied to all entities in the same layer #219 flows need stronger regression protection at both renderer-unit and viewer-e2e levels.

What Changed

• packages/cad-simple-viewer/src/view/AcTrView2d.ts now remaps inherited block materials via getLayerBoundMaterial, resolves effective layer traits, and promotes layer-0 color binding when other ByLayer bindings are present.
• packages/three-renderer/src/renderer/AcTrRenderer.ts and packages/three-renderer/src/style/AcTrStyleManager.ts replace remapMaterialLayer with getLayerBoundMaterial(material, layerName, layerTraits?).
• packages/three-renderer/src/style/AcTrMaterialManager.ts now applies inherited layer traits only for flagged ByLayer attributes and stores/reads granular metadata flags.
• packages/three-renderer/src/style/AcTrMaterialMetadata.ts adds typed metadata helpers (getMaterialMetadata, setMaterialMetadata, hasByLayerBinding), exported via packages/three-renderer/src/index.ts.
• packages/three-renderer/__tests__/AcTrStyleManager.spec.ts updates remap tests and adds a case that refreshes ByLayer color even when target layer is unchanged.
• packages/cad-viewer-example/e2e/tests/smoke.spec.ts adds a regression test using new fixture packages/cad-viewer-example/e2e/fixtures/block-color.dxf and snapshot block-layer0-bylayer-inherit-chromium-win32.png.
• Branch baseline (main..fix/219) also includes broader issue layer color change not applied to all entities in the same layer #219 refactors across viewer/renderer/layer UI files plus dependency/lockfile adjustments.

Risks / Notes

• External/custom code reading material.userData.isByLayer may need migration to granular flags.
• API consumers using remapMaterialLayer must migrate to getLayerBoundMaterial.
• The added DXF fixture (~15,952 lines) and screenshot snapshot increase review noise and repository size.

Breaking Changes

• AcTrRenderer/AcTrStyleManager layer-remap API renamed from remapMaterialLayer to getLayerBoundMaterial.
• Material metadata contract now relies on isByLayerColor, isByLayerLineType, isByLayerLineWeight, and isByLayerTransparency instead of a single isByLayer.