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/services/adapters/duplicates.ts

@@ -0,0 +1,41 @@
+/**
+ * Adapter that shapes PhotoPrism's `q=stack:true` photo list into a
+ * `DuplicateGroup[]` the UI consumes. Mirrors mule-image's
+ * `DuplicateGroup` interface so the view code stays declarative.
+ *
+ * PhotoPrism's `/photos?merged=true` inlines `Files[]` on each row
+ * already — no follow-up GET per group needed (confirmed against
+ * photoprism/photoprism:latest, May 2026).
+ */
+
+import { listPhotos } from '$lib/services/photoprism';
+import type { PpFile, PpPhoto } from '$lib/types/photoprism';
+
+export interface DuplicateGroup {
+	/** The Photo record that owns this stack. Carries marks, keywords,
+	 *  taken_at — everything the metadata sidebar reads off of. */
+	photo: PpPhoto;
+	/** The variants the user picks among. Always 2+ entries; groups with
+	 *  a single file are filtered out (PhotoPrism shouldn't return them
+	 *  for `stack:true` anyway, but the guard is cheap). */
+	files: PpFile[];
+	/** Pre-selected "keep this" file = the one PhotoPrism marks Primary.
+	 *  The view starts with this highlighted and updates it on click. */
+	bestFileUid: string;
+}
+
+export async function listDuplicateGroups(): Promise<DuplicateGroup[]> {
+	const photos = await listPhotos({
+		q: 'stack:true',
+		count: 200,
+		merged: true,
+		order: 'newest'
+	});
+	return photos
+		.filter((p) => (p.Files?.length ?? 0) > 1)
+		.map((p) => {
+			const files = p.Files ?? [];
+			const primary = files.find((f) => f.Primary) ?? files[0];
+			return { photo: p, files, bestFileUid: primary.UID };
+		});
+}