feat: add s3 storage provider integration

docs/storage_provider.md

@@ -0,0 +1,32 @@
+# Storage Provider Setup
+
+This project supports local filesystem storage for development/tests and an S3-compatible provider (AWS S3/MinIO) for production.
+
+## Local (dev/test)
+
+Use local storage for tests and quick development.
+
+```toml
+[Storage]
+Type = "local"
+LocalPath = "./storage"
+Secret = "your-storage-secret"
+BaseURL = "http://localhost:8080/t/<tenantCode>/v1/storage"
+```
+
+Note: `BaseURL` should include the tenant code because storage routes are tenant-scoped.
+
+## S3/MinIO (example)
+
+```toml
+[Storage]
+Type = "s3"
+AccessKey = "minioadmin"
+SecretKey = "minioadmin"
+Region = "us-east-1"
+Bucket = "quyun-assets"
+Endpoint = "http://127.0.0.1:9000"
+PathStyle = true
+```
+
+For AWS S3, set `Endpoint` with `https://` (e.g., `https://s3.amazonaws.com`) and keep `PathStyle` as `false` unless your provider requires path-style access.