feat(report): align MarkdownReport columns for readable ASCII/markdown output

benchmark_cherrypick/lib/cli/report/markdown_report.dart

@@ -0,0 +1,43 @@
+import 'report_generator.dart';
+
+class MarkdownReport extends ReportGenerator {
+  @override
+  final List<String> keys = [
+    'benchmark','chainCount','nestingDepth','mean_us','median_us','stddev_us',
+    'min_us','max_us','trials','memory_diff_kb','delta_peak_kb','peak_rss_kb'
+  ];
+  static const nameMap = {
+    'Universal_UniversalBenchmark.registerSingleton':'RegisterSingleton',
+    'Universal_UniversalBenchmark.chainSingleton':'ChainSingleton',
+    'Universal_UniversalBenchmark.chainFactory':'ChainFactory',
+    'Universal_UniversalBenchmark.chainAsync':'AsyncChain',
+    'Universal_UniversalBenchmark.named':'Named',
+    'Universal_UniversalBenchmark.override':'Override',
+  };
+  @override
+  String render(List<Map<String, dynamic>> rows) {
+    final headers = [
+      'Benchmark', 'Chain Count', 'Depth', 'Mean (us)', 'Median', 'Stddev', 'Min', 'Max', 'N', 'ΔRSS(KB)', 'ΔPeak(KB)', 'PeakRSS(KB)'
+    ];
+    final header = '| ' + headers.join(' | ') + ' |';
+    final divider = '|' + List.filled(headers.length, '---').join('|') + '|';
+    final dataRows = rows.map((r) {
+      final readableName = nameMap[r['benchmark']] ?? r['benchmark'];
+      return [
+        readableName,
+        r['chainCount'],
+        r['nestingDepth'],
+        r['mean_us'],
+        r['median_us'],
+        r['stddev_us'],
+        r['min_us'],
+        r['max_us'],
+        r['trials'],
+        r['memory_diff_kb'],
+        r['delta_peak_kb'],
+        r['peak_rss_kb'],
+      ].map((cell) => cell.toString().padRight(10)).join(' | ');
+    }).map((row) => '| $row |').toList();
+    return ([header, divider] + dataRows).join('\n');
+  }
+}