Match stat-table header background with Legend (Diff Detail) design

Add inline background:#f5f5f7 (TH_BG_DEFAULT) to Summary and IL Cache
Stats table <th> elements, matching the Legend (Diff Detail) header
styling.

https://claude.ai/code/session_01HnKMFA576NFwa2RzB8vCqE

Author: claude

Services/HtmlReport/HtmlReportGenerateService.Sections.cs

@@ -494,7 +494,7 @@ private void AppendSummarySection(StringBuilder sb, IReadOnlyConfigSettings conf
         {
             sb.AppendLine($"<h2 class=\"section-heading\">{I18n("Summary", "サマリー")}</h2>");
             sb.AppendLine("<table class=\"stat-table\">");
-            sb.AppendLine("  <thead><tr><th>Category</th><th>Count</th></tr></thead>");
+            sb.AppendLine($"  <thead><tr><th style=\"background:{TH_BG_DEFAULT}\">Category</th><th style=\"background:{TH_BG_DEFAULT}\">Count</th></tr></thead>");
             sb.AppendLine("  <tbody>");
             var stats = _fileDiffResultLists.SummaryStatistics;
             if (config.ShouldIncludeIgnoredFiles)
@@ -513,7 +513,7 @@ private static void AppendILCacheStatsSection(StringBuilder sb, ILCache ilCache)
             var stats = ilCache.GetReportStats();
             sb.AppendLine($"<h2 class=\"section-heading\">{I18n("IL Cache Stats", "IL キャッシュ統計")}</h2>");
             sb.AppendLine("<table class=\"stat-table\">");
-            sb.AppendLine("  <thead><tr><th>Metric</th><th>Value</th></tr></thead>");
+            sb.AppendLine($"  <thead><tr><th style=\"background:{TH_BG_DEFAULT}\">Metric</th><th style=\"background:{TH_BG_DEFAULT}\">Value</th></tr></thead>");
             sb.AppendLine("  <tbody>");
             sb.AppendLine($"    <tr><td class=\"stat-label\">Hits</td><td class=\"stat-value\">{stats.Hits}</td></tr>");
             sb.AppendLine($"    <tr><td class=\"stat-label\">Misses</td><td class=\"stat-value\">{stats.Misses}</td></tr>");

doc/samples/diff_report.html

@@ -761,7 +761,7 @@ <h2 style="color:#0051c3">[ * ] Modified Files (14)</h2>
 </div>
 <h2 class="section-heading">Summary</h2>
 <table class="stat-table">
-  <thead><tr><th>Category</th><th>Count</th></tr></thead>
+  <thead><tr><th style="background:#f5f5f7">Category</th><th style="background:#f5f5f7">Count</th></tr></thead>
   <tbody>
     <tr><td class="stat-label">Ignored</td><td class="stat-value">3</td></tr>
     <tr><td class="stat-label">Unchanged</td><td class="stat-value">5</td></tr>
@@ -773,7 +773,7 @@ <h2 class="section-heading">Summary</h2>
 </table>
 <h2 class="section-heading">IL Cache Stats</h2>
 <table class="stat-table">
-  <thead><tr><th>Metric</th><th>Value</th></tr></thead>
+  <thead><tr><th style="background:#f5f5f7">Metric</th><th style="background:#f5f5f7">Value</th></tr></thead>
   <tbody>
     <tr><td class="stat-label">Hits</td><td class="stat-value">42</td></tr>
     <tr><td class="stat-label">Misses</td><td class="stat-value">8</td></tr>