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.

app/src/adapter/sveltekit/sveltekit.adapter.spec.ts

@@ -9,7 +9,7 @@ afterAll(enableConsoleLog);
 
 describe("sveltekit adapter", () => {
    adapterTestSuite(bunTestRunner, {
-      makeApp: sveltekit.getApp,
-      makeHandler: (c, a) => (request: Request) => sveltekit.serve(c, a)({ request }),
+      makeApp: (c, a) => sveltekit.getApp(c, a ?? ({} as any)),
+      makeHandler: (c, a) => (request: Request) => sveltekit.serve(c, a ?? ({} as any))({ request }),
    });
 });