controller v0.272.0: the backup page says when a whole-box backup does not fit (R-685); R-671, R-670, R-677

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

controller/internal/stacks/ladder.go

@@ -225,5 +225,5 @@ func loadMetadataFile(path string) (Metadata, error) {
 	if err := os.WriteFile(filepath.Join(tmp, ".felhom.yml"), data, 0o600); err != nil {
 		return Metadata{}, err
 	}
-	return LoadMetadata(tmp), nil
+	return LoadProbeMetadata(tmp), nil // R-670
 }