feat: PhotoPrism M0 bring-up — compose stack, web client, sidecar, migrate

Replace the legacy mule-image backend with PhotoPrism plus a thin
SvelteKit client and a Node sidecar for endpoints PhotoPrism doesn't
expose (file rename), and add a two-phase migrator (metadata via PUT,
heaps → albums) for the existing Postgres library.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/src/lib/utils.ts

@@ -0,0 +1,10 @@
+import { clsx, type ClassValue } from 'clsx';
+import { twMerge } from 'tailwind-merge';
+
+/**
+ * shadcn-svelte's canonical class composer: merge tailwind classes,
+ * de-duplicate conflicts (last one wins for the same utility group).
+ */
+export function cn(...inputs: ClassValue[]): string {
+	return twMerge(clsx(inputs));
+}