Set up S3 testing infrastructure for backup implementation

- Add gofakes3 for in-process S3-compatible test server
- Create test server that runs on localhost:9999 with temp directory
- Implement basic S3 client wrapper with standard operations
- Add comprehensive tests for blob and metadata storage patterns
- Test cleanup properly removes temporary directories
- Use AWS SDK v2 for S3 operations with proper error handling

internal/s3/client_test.go

@@ -0,0 +1,98 @@
+package s3_test
+
+import (
+	"bytes"
+	"context"
+	"io"
+	"testing"
+
+	"git.eeqj.de/sneak/vaultik/internal/s3"
+)
+
+func TestClient(t *testing.T) {
+	ts := NewTestServer(t)
+	defer func() {
+		if err := ts.Cleanup(); err != nil {
+			t.Errorf("cleanup failed: %v", err)
+		}
+	}()
+
+	ctx := context.Background()
+
+	// Create client
+	client, err := s3.NewClient(ctx, s3.Config{
+		Endpoint:        testEndpoint,
+		Bucket:          testBucket,
+		Prefix:          "test-prefix/",
+		AccessKeyID:     testAccessKey,
+		SecretAccessKey: testSecretKey,
+		Region:          testRegion,
+	})
+	if err != nil {
+		t.Fatalf("failed to create client: %v", err)
+	}
+
+	// Test PutObject
+	testKey := "foo/bar.txt"
+	testData := []byte("test data")
+	err = client.PutObject(ctx, testKey, bytes.NewReader(testData))
+	if err != nil {
+		t.Fatalf("failed to put object: %v", err)
+	}
+
+	// Test GetObject
+	reader, err := client.GetObject(ctx, testKey)
+	if err != nil {
+		t.Fatalf("failed to get object: %v", err)
+	}
+	defer func() {
+		if err := reader.Close(); err != nil {
+			t.Errorf("failed to close reader: %v", err)
+		}
+	}()
+
+	data, err := io.ReadAll(reader)
+	if err != nil {
+		t.Fatalf("failed to read data: %v", err)
+	}
+
+	if !bytes.Equal(data, testData) {
+		t.Errorf("data mismatch: got %q, want %q", data, testData)
+	}
+
+	// Test HeadObject
+	exists, err := client.HeadObject(ctx, testKey)
+	if err != nil {
+		t.Fatalf("failed to head object: %v", err)
+	}
+	if !exists {
+		t.Error("expected object to exist")
+	}
+
+	// Test ListObjects
+	keys, err := client.ListObjects(ctx, "foo/")
+	if err != nil {
+		t.Fatalf("failed to list objects: %v", err)
+	}
+	if len(keys) != 1 {
+		t.Errorf("expected 1 key, got %d", len(keys))
+	}
+	if keys[0] != testKey {
+		t.Errorf("unexpected key: got %s, want %s", keys[0], testKey)
+	}
+
+	// Test DeleteObject
+	err = client.DeleteObject(ctx, testKey)
+	if err != nil {
+		t.Fatalf("failed to delete object: %v", err)
+	}
+
+	// Verify deletion
+	exists, err = client.HeadObject(ctx, testKey)
+	if err != nil {
+		t.Fatalf("failed to head object after deletion: %v", err)
+	}
+	if exists {
+		t.Error("expected object to not exist after deletion")
+	}
+}