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/routes/+layout.ts

@@ -0,0 +1,4 @@
+// SPA mode: disable SSR / prerendering across the app. The Svelte client
+// talks directly to PhotoPrism's REST + WebSocket; no server runtime needed.
+export const ssr = false;
+export const prerender = false;