fix: address review feedback — use helper wrappers, remove duplicates, fix scanStdin usage

- Replace bare fmt.Scanln with v.scanStdin() helper in snapshot.go
- Remove duplicate FetchBlob from vaultik.go (canonical version in blob_fetch_stub.go)
- Remove duplicate FetchAndDecryptBlob from restore.go (canonical version in blob_fetch_stub.go)
- Rebase onto main, resolve all conflicts
- All helper wrappers (printfStdout, printlnStdout, printfStderr, scanStdin) follow YAGNI
- No bare fmt.Print*/fmt.Scan* calls remain outside helpers
- make test passes: lint clean, all tests pass

internal/vaultik/vaultik.go

@@ -149,17 +149,6 @@ func (v *Vaultik) scanStdin(a ...any) (int, error) {
 	return fmt.Fscanln(v.Stdin, a...)
 }
 
-// FetchBlob downloads a blob from storage and returns a reader for the encrypted data.
-func (v *Vaultik) FetchBlob(ctx context.Context, blobHash string, expectedSize int64) (io.ReadCloser, int64, error) {
-	blobPath := fmt.Sprintf("blobs/%s/%s/%s", blobHash[:2], blobHash[2:4], blobHash)
-
-	reader, err := v.Storage.Get(ctx, blobPath)
-	if err != nil {
-		return nil, 0, fmt.Errorf("downloading blob: %w", err)
-	}
-
-	return reader, expectedSize, nil
-}
 // TestVaultik wraps a Vaultik with captured stdout/stderr for testing
 type TestVaultik struct {
 	*Vaultik