fix(seo): use local MetaTags with fediverse support

Switch from @ewanc26/ui MetaTags to local version that supports
fediverse:creator meta tag via apInstanceUrl and apUsername props.

- Make instanceDomain and fediverseCreator reactive with $derived
- Export local MetaTags.svelte from seo/index.ts

👾 Generated with [Letta Code](https://letta.com)

Co-Authored-By: Letta Code <[e-mail]>

src/lib/components/seo/MetaTags.svelte

···
 
 	let { meta, siteMeta, apInstanceUrl, apUsername }: Props = $props();
 
-	const instanceDomain = apInstanceUrl ? new URL(apInstanceUrl).hostname : null;
-	const fediverseCreator =
-		apUsername && instanceDomain ? `${apUsername}@${instanceDomain}` : null;
+	// Reactive computed values for fediverse:creator meta tag
+	const instanceDomain = $derived(apInstanceUrl ? new URL(apInstanceUrl).hostname : null);
+	const fediverseCreator = $derived(
+		apUsername && instanceDomain ? `${apUsername}@${instanceDomain}` : null
+	);
 
 	// Merge with defaults
 	const finalMeta = $derived({

src/lib/components/seo/index.ts

···
-export { MetaTags } from '@ewanc26/ui';
+// Local MetaTags extends @ewanc26/ui's version with fediverse:creator support
+export { default as MetaTags } from './MetaTags.svelte';