Add lower-corner layouts, custom blur backgrounds, and classic blur fill.

Ship composition families, optional background images for lower-corner templates, and an optional blurred cover fill for classic letterbox.

prisma/migrations/20260806230000_add_blur_fill/migration.sql

@@ -0,0 +1,2 @@
+-- AlterTable
+ALTER TABLE "JobItem" ADD COLUMN "blurFill" BOOLEAN NOT NULL DEFAULT false;