Add Chromium-only Blender WebEngine parity work

docs/status/W-034.md

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+# W-034 Status
+
+status: done_current_scope
+task: 导出材质、贴图和颜色
+
+## Implemented
+
+The SceneIR contract includes Principled-compatible base color, roughness,
+metallic, emission, alpha and IOR fields. The native reader walks embedded
+Principled node inputs, collects Image Texture IDs, and emits warnings for
+linked inputs or unsupported nodes. Blender Image datablocks export stable
+asset IDs, MIME guesses, generated dimensions and the original (possibly
+`//`-relative) source path without embedding base64 pixels. The EngineWorker
+exposes a local `requestAsset` metadata path for external and
+packed-unavailable assets. The Three adapter applies the exported material
+color, metalness, roughness, emission and alpha to local materials.
+
+## Accepted bounded scope
+
+Material slots can be created, removed and assigned to selected faces through
+Blender Main. The Web authoring surface writes Principled values and creates a
+limited `Principled -> Output`, `Image Texture`, `Normal Map` and `UV Map` graph.
+PNG/JPEG imports become packed Blender Image datablocks without allocating a
+headless ImBuf, and active UV-map/planar/cube unwrap operations round-trip.
+Packed bytes remain available through the asset API and are covered by the
+UDIM/generated/linked/corrupt resource matrix.
+
+Arbitrary node graphs and renderer-specific shader execution are deliberately
+outside this bounded contract; unsupported nodes are reported by SceneIR.