Add end-to-end integration tests for Vaultik

- Create comprehensive integration tests with mock S3 client
- Add in-memory filesystem and SQLite database support for testing
- Test full backup workflow including chunking, packing, and uploading
- Add test to verify encrypted blob content
- Fix scanner to use afero filesystem for temp file cleanup
- Demonstrate successful backup and verification with mock dependencies

internal/snapshot/scanner.go

@@ -676,7 +676,7 @@ func (s *Scanner) handleBlobReady(blobWithReader *blob.BlobWithReader) error {
 		if err := blobWithReader.TempFile.Close(); err != nil {
 			log.Fatal("Failed to close temp file", "file", tempName, "error", err)
 		}
-		if err := os.Remove(tempName); err != nil {
+		if err := s.fs.Remove(tempName); err != nil {
 			log.Fatal("Failed to remove temp file", "file", tempName, "error", err)
 		}
 	}