feat(storage): add S3 backend support and advanced upload limits

- Introduce S3-compatible storage backend support using minio-go.
- Add configuration options for local storage limits, box limits, and rate limiting.
- Implement storage backend selection (local vs S3) for anonymous and registered users.
- Add an `/admin/storage` management interface.
- Update documentation and environment examples with the new configuration variables.

backend/libs/services/upload_test.go

@@ -2,6 +2,7 @@ package services
 
 import (
 	"bytes"
+	"context"
 	"io"
 	"log/slog"
 	"mime/multipart"
@@ -93,6 +94,64 @@ func TestUserActiveStorageUsedIgnoresExpiredBoxes(t *testing.T) {
 	}
 }
 
+func TestLocalStorageBackendAndLegacyFallback(t *testing.T) {
+	service := newTestUploadService(t)
+	result := createTestBox(t, service, "file.txt", "hello")
+	box := getTestBox(t, service, result.BoxID)
+	if service.BoxStorageBackendID(box) != StorageBackendLocal {
+		t.Fatalf("BoxStorageBackendID = %q", service.BoxStorageBackendID(box))
+	}
+	if box.Files[0].ObjectKey == "" {
+		t.Fatalf("new file did not store object key")
+	}
+	object, err := service.OpenFileObject(testContext(), box, box.Files[0])
+	if err != nil {
+		t.Fatalf("OpenFileObject returned error: %v", err)
+	}
+	data, err := io.ReadAll(object.Body)
+	object.Body.Close()
+	if err != nil {
+		t.Fatalf("ReadAll returned error: %v", err)
+	}
+	if string(data) != "hello" {
+		t.Fatalf("object body = %q", string(data))
+	}
+
+	box.StorageBackendID = ""
+	box.Files[0].ObjectKey = ""
+	object, err = service.OpenFileObject(testContext(), box, box.Files[0])
+	if err != nil {
+		t.Fatalf("legacy OpenFileObject returned error: %v", err)
+	}
+	object.Body.Close()
+}
+
+func TestContaboStorageConfigAllowsDisplayNamesWithSpaces(t *testing.T) {
+	service := newTestUploadService(t)
+	cfg, err := service.Storage().CreateS3Backend(StorageBackendConfig{
+		Provider:  StorageProviderContabo,
+		Name:      "Contabo main",
+		Endpoint:  "https://eu2.contabostorage.com",
+		Region:    "EU",
+		Bucket:    "My Main Bucket",
+		AccessKey: "access",
+		SecretKey: "secret",
+	})
+	if err != nil {
+		t.Fatalf("CreateS3Backend returned error: %v", err)
+	}
+	if cfg.Provider != StorageProviderContabo || !cfg.UseSSL || !cfg.PathStyle {
+		t.Fatalf("contabo config was not normalized: %+v", cfg)
+	}
+	if cfg.Bucket != "My Main Bucket" {
+		t.Fatalf("bucket = %q", cfg.Bucket)
+	}
+}
+
+func testContext() context.Context {
+	return context.Background()
+}
+
 func newTestUploadService(t *testing.T) *UploadService {
 	t.Helper()
 	service, err := NewUploadService(1024*1024, t.TempDir(), "http://example.test", slog.New(slog.NewTextHandler(io.Discard, nil)))