allow importing of libraries via URL, update db schema

backend/prisma/migrations/20251124220546_add_library_model/migration.sql

@@ -0,0 +1,7 @@
+-- CreateTable
+CREATE TABLE "Library" (
+    "id" TEXT NOT NULL PRIMARY KEY DEFAULT 'default',
+    "items" TEXT NOT NULL DEFAULT '[]',
+    "createdAt" DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "updatedAt" DATETIME NOT NULL
+);