fix: polish public sharing page and landing page

- Link "POWERED BY CRUMBS" to crumbs.bretzel.app
- Add dedicated error page for (share) group without "Back to notes"
- Update landing page Note Sharing card to mention public links

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/routes/(share)/+error.svelte

@@ -0,0 +1,17 @@
+<script lang="ts">
+	import { page } from '$app/state';
+</script>
+
+<svelte:head>
+	<title>Not Found - Crumbs</title>
+</svelte:head>
+
+<div class="w-full max-w-sm rounded-sm border border-[var(--border)] bg-[var(--bg-surface)] p-8 text-center">
+	<img src="/favicon.svg" alt="Crumbs" class="mx-auto h-12 w-12" />
+	<h1 class="mt-4 font-['Press_Start_2P'] text-xl text-[var(--primary)]">
+		{page.status}
+	</h1>
+	<p class="mt-4 text-sm text-[var(--text-muted)]">
+		{page.error?.message ?? 'This shared note does not exist or has been removed.'}
+	</p>
+</div>

src/routes/(share)/s/[token]/+page.svelte

@@ -112,7 +112,7 @@
 
 	<div class="mt-6 text-center">
 		<a
-			href="https://github.com/bretzel-app/crumbs"
+			href="https://crumbs.bretzel.app"
 			target="_blank"
 			rel="noopener noreferrer"
 			class="font-['Press_Start_2P'] text-[8px] tracking-wider text-[var(--text-muted)] hover:text-[var(--primary)] transition-colors"

website/index.html

@@ -173,7 +173,7 @@
 						<svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><circle cx="18" cy="5" r="3"/><circle cx="6" cy="12" r="3"/><circle cx="18" cy="19" r="3"/><line x1="8.59" y1="13.51" x2="15.42" y2="17.49"/><line x1="15.41" y1="6.51" x2="8.59" y2="10.49"/></svg>
 					</div>
 					<h3>Note Sharing</h3>
-					<p>Share notes with other users on your instance. Full collaboration with per-user pins and archives.</p>
+					<p>Share notes via public link or with other users. Full collaboration with per-user pins and archives.</p>
 				</div>
 
 				<!-- Version History -->