feat(wallet.svelte): integrate pkpWallet into state store

- Initialize pkpWallet with null value inside the component store.
- Update store's pkpWallet upon successful wallet connection.
- Reflect pkpWallet value reactively in the UI.

BREAKING CHANGE: The pkpWallet now resides in the component's store and should be accessed as $store.pkpWallet.

src/lib/components/HelloEarth/HelloEarth.svelte

@@ -5,14 +5,13 @@
 	import { onMount } from 'svelte';
 
 	const store = getComponentStore(id);
-	$: console.log('store:', $store);
 
 	export let helloEarthAlert;
 
 	onMount(async () => {
 		helloEarthAlert.alertMe();
-		console.log('hello Earth');
+		console.log('should alerted by now');
 	});
 </script>
 
-<div class="p-12 bg-blue-400">Hello Earth {JSON.stringify($store)}</div>
+<div class="p-12 bg-blue-400">Hello Earth {JSON.stringify($store.pkpWallet.address)}</div>