Serve the styleguide's images and links locally

The styleguide loaded 42 images from picsum.photos and linked demo items to
daisyui.com. It now uses six small SVG landscapes in wwwroot/imgs/styleguide/
(the diff demo greys one with the grayscale utility), and its demo links stay on
/styleguide.

It also gains a carousel demo with navigation and indicators.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

Components/Styleguide/MockupSection.razor

@@ -36,7 +36,7 @@
 				<div class="grid h-full place-content-center bg-neutral text-neutral-content">It's Glowtime.</div>
 			</DMockupPhone>
 			<DMockupPhone class="max-w-56 border-primary">
-				<img src="https://picsum.photos/seed/phone/462/978" alt="wallpaper" />
+				<img src="imgs/styleguide/scene-5.svg" alt="wallpaper" />
 			</DMockupPhone>
 		</div>
 	</section>