feat(storage): add S3/R2 abstraction with local Rustfs dev

- Add backend/internal/s3/ with build-tag pattern (dev vs prod)
- Dev: Uses local Rustfs container (S3-compatible)
- Prod: Stub for R2 Cloudflare (add AWS SDK to implement)
- Add S3 env vars to .env.example and .env
- Add Rustfs service to compose.yml
- Add Rustfs reset to local-dev-2.sh (wipes data on each run)

.env.example

@@ -11,3 +11,19 @@ POSTGRES_HOST=postgres
 POSTGRES_PORT=5432
 
 JWT_SECRET_KEY="a-very-secret-key-that-should-be-in-env"
+
+# S3/R2 Configuration (for image storage)
+# Dev: Uses local Rustfs container (see compose.yml)
+# Prod: Use Cloudflare R2 credentials
+S3_ENDPOINT=http://localhost:9000
+S3_ACCESS_KEY=minioadmin
+S3_SECRET_KEY=minioadmin
+S3_BUCKET=crussell
+
+# Prod: Uncomment and fill these for R2
+# R2_ENDPOINT=https://<account-id>.r2.cloudflarestorage.com
+# R2_ACCESS_KEY=<your-access-key>
+# R2_SECRET_KEY=<your-secret-key>
+# R2_BUCKET=crussell
+# R2_PUBLIC_URL=https://pub-<your-domain>.r2.dev
+# AWS_REGION=auto