Serve source map in Lookout UI build (#4434)

This allows error monitoring applications to deliver more informative
error messages about the origin of the error, and so improves the
ability to debug problems.

Author: mauriceyap

internal/lookoutui/vite.config.mts

@@ -59,5 +59,6 @@ export default defineConfig({
   },
   build: {
     outDir: "build",
+    sourcemap: true,
   },
 })