style: strip to grayscale wireframe

- Remap all non-gray colors (blue, green, red, purple, slate) to gray
  equivalents via Tailwind v4 @theme overrides in layout.css
- Zero out all border-radius values (square everything)
- Zero out all shadow values (no depth)
- Disable all transitions and animations globally
- Change theme-color meta tag from purple (#7B2D8E) to gray (#6b7280)
- Clean up undefined 'underlined' class and typo bg-grey-200

src/routes/+error.svelte

@@ -6,11 +6,8 @@
 <Window>
 	{#if $page.status === 403}
 		<h1>Not Authorized</h1>
-		<p>
-			You don't have permission to view this page. Click <a
-				href="/"
-				class="underlined text-blue-600">here</a
-			> to return home.
-		</p>
+      <p>
+        You don't have permission to view this page. <a href="/">Go home</a>.
+      </p>
 	{/if}
 </Window>