fix(engine): declare builtin.ts as side-effectful to prevent tree-shaking

sideEffects:false told bundlers the import './charts/builtin' side-effect in compile.ts was safe to drop. Vite would strip it when resolving the engine via source alias, leaving the renderer registry empty. All chart types returned empty marks with no error.

Declare builtin.ts (and dist/index.js) as side-effectful so bundlers keep the registration import.

Author: rileyhilliard

packages/engine/package.json

@@ -30,7 +30,7 @@
     "dist",
     "src"
   ],
-  "sideEffects": false,
+  "sideEffects": ["./src/charts/builtin.ts", "./dist/index.js"],
   "keywords": [
     "chart",
     "visualization",