chore(canvas): enable Turbopack for dev server — faster HMR

next dev --turbopack for significantly faster dev server startup
and hot module replacement. Build script unchanged (Turbopack for
next build is still experimental).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

canvas/package.json

@@ -3,7 +3,7 @@
   "version": "0.1.0",
   "private": true,
   "scripts": {
-    "dev": "next dev",
+    "dev": "next dev --turbopack",
     "build": "next build",
     "start": "next start",
     "lint": "next lint",