Add better-auth integration and update dependencies in package.json and bun.lock

apps/web/src/routes/api/auth/[...all]/+server.ts

@@ -0,0 +1,3 @@
+import { createSvelteKitHandler } from "@mmailaender/convex-better-auth-svelte/sveltekit";
+
+export const { GET, POST } = createSvelteKitHandler();