feat(canvas): import DWG/DXF CAD drawings as canvas assets

Accept DWG and DXF files (up to 24 MB) through the canvas asset picker and
drag-and-drop. Conversion runs locally in a browser worker via acad-ts,
uploads a sanitized derived SVG, and leaves the source file untouched. DXF
covers ASCII and binary drawings; DWG covers AutoCAD R14 through 2018.

Rename the image-only upload input/handler to a generic canvas asset flow,
add vector-image node detection, tag imported SVGs as vector-image nodes,
localize CAD import status/error messages, and switch the Next build to the
webpack compiler so the worker bundles correctly. Add a node --test suite
covering CAD conversion and vector image helpers.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

README.md

@@ -1,6 +1,6 @@
 # img-infinite-canvas
 
-Moteva 风格的 AI 设计工作台复刻 MVP：主页 Prompt 创建项目，项目页提供无限画布、节点拖拽、缩放平移、右侧设计对话、历史回放、图片资产上传、项目保存与再生成。
+Moteva 风格的 AI 设计工作台复刻 MVP：主页 Prompt 创建项目，项目页提供无限画布、节点拖拽、缩放平移、右侧设计对话、历史回放、图片与 DWG/DXF 图纸导入、项目保存与再生成。
 
 ## Stack
 
@@ -31,6 +31,10 @@ pnpm dev
 
 Open `http://localhost:5173`. Next.js rewrites `/api` to `http://localhost:8888` in development. `pnpm build` runs `next build` and `vite build`, producing gzip assets in `frontend/dist`.
 
+## CAD Import
+
+The canvas asset picker and drag-and-drop surface accept DWG and DXF files up to 24 MB. Conversion runs locally in a browser worker, uploads a sanitized derived SVG, and leaves the source file unchanged. DXF supports ASCII and binary drawings; DWG supports AutoCAD R14 through AutoCAD 2018 format families.
+
 ## Cache Config
 
 Default in-memory cache: