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

apps/backend/src/presets/presets.controller.ts

@@ -0,0 +1,49 @@
+import { Controller, Get } from "@nestjs/common"
+import { ApiOkResponse, ApiOperation, ApiTags } from "@nestjs/swagger"
+import {
+  CUSTOM_TRANSFORM_CONFIG,
+  IMAGE_PRESETS,
+  loadAllowedSourceHostsFromEnv,
+  parseBooleanFlag,
+  type ImagePreset,
+} from "@image-platform/image-config"
+
+import { PresetsResponseDto } from "./presets.dto"
+
+@ApiTags("presets")
+@Controller("presets")
+export class PresetsController {
+  @Get()
+  @ApiOperation({
+    summary: "получить доступные presets и custom config",
+    description: "Возвращает статический config presets, custom transform limits и mock allowlist source hosts.",
+  })
+  @ApiOkResponse({ description: "Конфигурация presets возвращена.", type: PresetsResponseDto })
+  getPresets(): PresetsResponseDto {
+    return {
+      allowedSourceHosts: [...loadAllowedSourceHostsFromEnv()],
+      custom: {
+        enabled: parseBooleanFlag(process.env.IMAGE_ALLOW_CUSTOM_TRANSFORMS, false),
+        formats: CUSTOM_TRANSFORM_CONFIG.formats,
+        maxHeight: CUSTOM_TRANSFORM_CONFIG.maxHeight,
+        maxWidth: CUSTOM_TRANSFORM_CONFIG.maxWidth,
+        quality: CUSTOM_TRANSFORM_CONFIG.quality,
+      },
+      presets: Object.entries(IMAGE_PRESETS).map(([name, preset]) => {
+        const config: ImagePreset = preset
+
+        return {
+          formats: config.formats,
+          height: config.height,
+          mode: config.mode,
+          name,
+          qualities: config.qualities,
+          quality: config.quality,
+          resize: config.resize,
+          width: config.width,
+          widths: config.widths,
+        }
+      }),
+    }
+  }
+}