feat: display app version in footer

Inject version from package.json at build time via Vite's define and
show it in the layout footer.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/app.d.ts

@@ -1,5 +1,7 @@
 // See https://svelte.dev/docs/kit/types#app.d.ts
 // for information about these interfaces
+declare const __APP_VERSION__: string;
+
 declare global {
 	namespace App {
 		// interface Error {}

src/routes/+layout.svelte

@@ -25,7 +25,7 @@
 	</main>
 
 	<footer class="pb-4 pt-8 text-center text-xs text-gray-400 lg:ml-64">
-		Crumbs by Bretzel &mdash; made with 🥨 in Strasbourg
+		Crumbs by Bretzel v{__APP_VERSION__} &mdash; made with 🥨 in Strasbourg
 	</footer>
 
 	<Toast />