feat: добавить генерацию image variants

- добавлен shared config presets, custom transforms и allowlist hosts
- реализованы Backend endpoints для assets, presets и variants
- добавлена orchestration через PostgreSQL, RabbitMQ, S3 и worker
- обновлён Gateway read-through flow с L1 cache и корректным Vary: Accept
- добавлена миграция resize_mode для variants lookup
- обновлены dev scripts, env template, lockfile и документация

packages/database/drizzle.config.ts

@@ -1,8 +1,14 @@
 import { defineConfig } from "drizzle-kit"
 
+const databaseUrl = process.env.DATABASE_URL
+
+if (!databaseUrl) {
+  throw new Error("DATABASE_URL is required")
+}
+
 export default defineConfig({
   dbCredentials: {
-    url: process.env.DATABASE_URL ?? "postgres://image:image-password@localhost:5433/image_platform",
+    url: databaseUrl,
   },
   dialect: "postgresql",
   out: "./drizzle",