feat: add SvelteKit adapter

Add framework adapter for SvelteKit with:
- `getApp()` - get bknd app instance
- `serve()` - request handler for hooks.server.ts

Usage in hooks.server.ts:
```typescript
import { serve } from "bknd/adapter/sveltekit";
import config from "../bknd.config";

const bkndHandler = serve(config);

export const handle = async ({ event, resolve }) => {
  if (event.url.pathname.startsWith("/api/")) {
    return bkndHandler(event);
  }
  return resolve(event);
};
```

Includes:
- Adapter implementation (app/src/adapter/sveltekit/)
- Test suite
- Working example (examples/sveltekit/)
- Package exports and types

examples/sveltekit/src/hooks.server.ts

@@ -0,0 +1,14 @@
+import type { Handle } from "@sveltejs/kit";
+import { serve } from "bknd/adapter/sveltekit";
+import config from "../bknd.config";
+
+const bkndHandler = serve(config);
+
+export const handle: Handle = async ({ event, resolve }) => {
+  // Handle bknd API requests
+  if (event.url.pathname.startsWith("/api/")) {
+    return bkndHandler(event);
+  }
+
+  return resolve(event);
+};