Add Chromium-only Blender WebEngine parity work

docs/status/W-073.md

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+# W-073 Status
+
+status: in_progress  
+task: 定义 Blender 三角面简化和 LOD 协议
+
+`web/protocol/simplify.ts` now defines versioned `SimplifyProfile`,
+`SimplifyResult` and `LODManifest` contracts. The profile validator keeps the
+Blender modifier modes separate:
+
+- `COLLAPSE` requires `ratio` in `(0, 1]` and supports triangle budget,
+  vertex-group weighting/inversion, triangulate, symmetry axis and tolerance.
+- `UNSUBDIV` requires a positive integer `iterations` and rejects collapse or
+  dissolve-only parameters.
+- `DISSOLVE_PLANAR` requires `angleLimit` in `[0, PI]`, with explicit
+  boundary delimit flags and dissolve-boundary handling.
+
+The parser also enforces non-negative source revisions and error codes for
+missing vertex groups, unsupported cross-mode fields, invalid budgets and LOD
+manifests whose triangle budgets do not decrease. A browser E2E test covers a
+valid collapse profile, a two-level manifest and the missing-vertex-group
+failure.
+
+The common profile now carries an explicit `attributePolicy`
+(`PRESERVE`/`RECOMPUTE_NORMALS`/`DROP`) and a validated `SkinSimplifyPolicy`
+with maximum influences, minimum weight, maximum position error and shape-key
+handling. Vertex-group and symmetry-only fields are conditionally optional, so
+the TypeScript contract and runtime validator no longer disagree when those
+features are disabled.
+
+The protocol is now exercised end-to-end by the native/WASM command path:
+`decimateMesh` validates `sourceMeshRevision`, returns a new SceneIR revision,
+and the browser-facing smoke checks topology counts, index bounds and attribute
+buffer lengths. Native Blender/WASM golden parity for all parameter
+combinations remains part of W-079; implementation of the declared skin policy
+remains W-076.