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>

frontend/tests/vectorImage.test.mjs

@@ -0,0 +1,28 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+
+import { isSvgSource, isVectorImageNode } from "../src/ui/lib/vectorImage.ts";
+
+const imageNode = {
+  id: "node-1",
+  type: "image",
+  title: "image.png",
+  x: 0,
+  y: 0,
+  width: 100,
+  height: 100,
+  content: "/uploads/image.png"
+};
+
+test("recognizes uploaded and CAD-derived SVG image nodes", () => {
+  assert.equal(isVectorImageNode({ ...imageNode, title: "drawing (DWG).svg" }), true);
+  assert.equal(isVectorImageNode({ ...imageNode, content: "/uploads/plan.svg?version=2" }), true);
+  assert.equal(isVectorImageNode({ ...imageNode, content: "data:image/svg+xml,%3Csvg/%3E" }), true);
+  assert.equal(isVectorImageNode({ ...imageNode, layerRole: "vectorized-image" }), true);
+  assert.equal(isVectorImageNode(imageNode), false);
+});
+
+test("recognizes encoded SVG paths without treating raster paths as vector", () => {
+  assert.equal(isSvgSource("https://assets.example.com/%E5%9B%BE%E7%BA%B8.svg#preview"), true);
+  assert.equal(isSvgSource("https://assets.example.com/image.png?format=svg"), false);
+});