refactor: load web UI assets with a relative URL to allow for hosting under a different path.

Might fix #53.

web/vite.config.ts

@@ -4,6 +4,7 @@ import react from "@vitejs/plugin-react-swc";
 // https://vitejs.dev/config/
 export default defineConfig({
   plugins: [react()],
+  base: "./",
   build: {
     rollupOptions: {
       // https://stackoverflow.com/q/69614671/vite-without-hash-in-filename#75344943