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>

mariadb/init/01-sidecar.sql

@@ -0,0 +1,25 @@
+-- Bootstraps the `mule_sidecar` database + user used by the Go sidecar
+-- service (per-user heap sharing + folder mutations, stood up in M4).
+--
+-- MariaDB runs every .sql in /docker-entrypoint-initdb.d ONCE, on first
+-- boot of a fresh data volume. Subsequent boots are no-ops.
+--
+-- The sidecar's MariaDB user is intentionally scoped to `mule_sidecar.*`
+-- only — it never has access to PhotoPrism's schema.
+
+CREATE DATABASE IF NOT EXISTS mule_sidecar
+  CHARACTER SET utf8mb4
+  COLLATE utf8mb4_unicode_ci;
+
+-- The password here is substituted at compose build time via envsubst,
+-- but MariaDB's init script doesn't expand vars in .sql files. So we use
+-- a literal placeholder that the user replaces locally — or, simpler,
+-- we let the M4 sidecar bring-up script create the user via SQL with the
+-- env-var password. Keeping a placeholder here makes the schema visible
+-- in source control without leaking creds.
+--
+-- TODO (M4): replace this block with an entrypoint that templates the
+-- password from $SIDECAR_DB_PASSWORD before MariaDB reads the file.
+CREATE USER IF NOT EXISTS 'sidecar'@'%' IDENTIFIED BY 'replace-at-m4-bringup';
+GRANT ALL PRIVILEGES ON mule_sidecar.* TO 'sidecar'@'%';
+FLUSH PRIVILEGES;