Change missing metadata log from Debug to Warn for visibility without --verbose

Per review feedback: missing unlocker metadata should produce a warning
visible in normal output, not hidden behind debug flags.

internal/vault/unlockers.go

@@ -213,7 +213,7 @@ func (v *Vault) ListUnlockers() ([]UnlockerMetadata, error) {
 				return nil, fmt.Errorf("failed to check if metadata exists for unlocker %s: %w", file.Name(), err)
 			}
 			if !exists {
-				secret.Debug("Skipping unlocker directory with missing metadata file", "directory", file.Name())
+				secret.Warn("Skipping unlocker directory with missing metadata file", "directory", file.Name())
 
 				continue
 			}