Add R2 image storage, upload endpoint, and CDN support

- Backend: R2StorageService, upload controller (POST /api/upload)
- Frontend: CDN url helper, NEXT_PUBLIC_CDN_URL build arg
- Deploy: pass R2 secrets from Woodpecker CI to containers via .env
- Docs: update CLAUDE.md with CDN and upload conventions

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

deploy/docker-compose.dev.yml

@@ -5,6 +5,7 @@ services:
       args:
         - NEXT_PUBLIC_POSTHOG_KEY=phc_pe0mP58n724h9eFxanbGIUsfMyS14gnAmr5tYez9V3Q
         - NEXT_PUBLIC_POSTHOG_HOST=https://eu.i.posthog.com
+        - NEXT_PUBLIC_CDN_URL=https://cdn.goodbrick.com.ua
     container_name: gb-dev-frontend
     restart: unless-stopped
     ports:
@@ -24,6 +25,11 @@ services:
     environment:
       - ASPNETCORE_ENVIRONMENT=Development
       - ConnectionStrings__Default=Host=postgres;Port=5432;Database=dev_db;Username=dev_user;Password=dev_pass_vB6nM3qP8yW2rT9k
+      - R2__AccountId=${R2_ACCOUNT_ID}
+      - R2__AccessKeyId=${R2_ACCESS_KEY_ID}
+      - R2__SecretAccessKey=${R2_SECRET_ACCESS_KEY}
+      - R2__BucketName=${R2_BUCKET_NAME:-goodbrick}
+      - R2__PublicUrl=https://cdn.goodbrick.com.ua
     networks:
       - app-network