fix(sveltekit): make adapter runtime-agnostic

Remove process.env default to support all SvelteKit runtimes
(Node, Cloudflare Workers, Vercel Edge, Deno). Users now pass
env explicitly via $env/dynamic/private.

examples/sveltekit/src/routes/+page.server.ts

@@ -1,9 +1,10 @@
 import type { PageServerLoad } from "./$types";
 import { getApp } from "bknd/adapter/sveltekit";
+import { env } from "$env/dynamic/private";
 import config from "../../bknd.config";
 
 export const load: PageServerLoad = async () => {
-  const app = await getApp(config);
+  const app = await getApp(config, env);
   const api = app.getApi();
 
   const todos = await api.data.readMany("todos");