AX Agent 좌측 패널 글자 크기 및 대화 목록 가독성 개선

- 좌측 사이드바 폭을 소폭 확장하고 헤더, 새 대화, 검색, 상단 필터, 보조 메뉴, 전체 삭제, 사용자 영역 타이포와 아이콘 크기 상향
- 대화 목록 그룹 헤더, 제목, 날짜, 실행 상태, 실행 요약, 편집 아이콘 크기와 카드 패딩 조정
- 좌측 패널 텍스트가 지나치게 작아 보이던 문제를 전체 시각 균형 기준으로 보정
- README 및 DEVELOPMENT 문서에 2026-04-05 23:09 (KST) 기준 변경 이력 반영

검증:
- dotnet build src/AxCopilot/AxCopilot.csproj -c Release -v minimal -p:OutputPath=bin\verify\ -p:IntermediateOutputPath=obj\verify\
- 경고 0 / 오류 0 확인

src/AxCopilot/Views/ChatWindow.xaml.cs

@@ -3187,10 +3187,10 @@ public partial class ChatWindow : Window
         var header = new TextBlock
         {
             Text = text,
-            FontSize = 10.5,
+            FontSize = 12,
             FontWeight = FontWeights.SemiBold,
             Foreground = (TryFindResource("SecondaryText") as Brush ?? Brushes.Gray),
-            Margin = new Thickness(8, 10, 0, 3)
+            Margin = new Thickness(8, 10, 0, 4)
         };
         ConversationPanel.Children.Add(header);
     }
@@ -3208,7 +3208,7 @@ public partial class ChatWindow : Window
                 ? new SolidColorBrush(Color.FromArgb(0x10, 0x4B, 0x5E, 0xFC))
                 : Brushes.Transparent,
             CornerRadius = new CornerRadius(5),
-            Padding = new Thickness(6, 3.5, 6, 3.5),
+            Padding = new Thickness(7, 4.5, 7, 4.5),
             Margin = isBranch ? new Thickness(10, 1, 0, 1) : new Thickness(0, 1, 0, 1),
             Cursor = Cursors.Hand
         };
@@ -3233,7 +3233,7 @@ public partial class ChatWindow : Window
         {
             Text = iconText,
             FontFamily = new FontFamily("Segoe MDL2 Assets"),
-            FontSize = 9.25,
+            FontSize = 10.5,
             Foreground = iconBrush,
             VerticalAlignment = VerticalAlignment.Center
         };
@@ -3248,7 +3248,7 @@ public partial class ChatWindow : Window
         var title = new TextBlock
         {
             Text = item.Title,
-            FontSize = 10,
+            FontSize = 11.75,
             FontWeight = isSelected ? FontWeights.SemiBold : FontWeights.Normal,
             Foreground = titleColor,
             TextTrimming = TextTrimming.CharacterEllipsis
@@ -3256,9 +3256,9 @@ public partial class ChatWindow : Window
         var date = new TextBlock
         {
             Text = item.UpdatedAtText,
-            FontSize = 7.6,
+            FontSize = 9,
             Foreground = dateColor,
-            Margin = new Thickness(0, 1, 0, 0)
+            Margin = new Thickness(0, 1.5, 0, 0)
         };
         stack.Children.Add(title);
         stack.Children.Add(date);
@@ -3269,10 +3269,10 @@ public partial class ChatWindow : Window
                 Text = _appState.ActiveTasks.Count > 0
                     ? $"진행 중 {_appState.ActiveTasks.Count}"
                     : "진행 중",
-                FontSize = 7.4,
+                FontSize = 8.8,
                 FontWeight = FontWeights.Medium,
                 Foreground = BrushFromHex("#4F46E5"),
-                Margin = new Thickness(0, 1, 0, 0),
+                Margin = new Thickness(0, 1.5, 0, 0),
             });
         }
         if (item.AgentRunCount > 0)
@@ -3282,11 +3282,11 @@ public partial class ChatWindow : Window
                 Text = item.FailedAgentRunCount > 0
                     ? $"실패 {item.FailedAgentRunCount} · {TruncateForStatus(item.LastAgentRunSummary, 26)}"
                     : $"실행 {item.AgentRunCount} · {TruncateForStatus(item.LastAgentRunSummary, 28)}",
-                FontSize = 7.45,
+                FontSize = 8.9,
                 Foreground = item.FailedAgentRunCount > 0
                     ? BrushFromHex("#B91C1C")
                     : (TryFindResource("SecondaryText") as Brush ?? Brushes.Gray),
-                Margin = new Thickness(0, 1, 0, 0),
+                Margin = new Thickness(0, 1.5, 0, 0),
                 TextTrimming = TextTrimming.CharacterEllipsis
             };
             if (!string.IsNullOrWhiteSpace(item.LastAgentRunSummary))
@@ -3307,7 +3307,7 @@ public partial class ChatWindow : Window
             {
                 Text = "\uE70F", // Edit
                 FontFamily = new FontFamily("Segoe MDL2 Assets"),
-                FontSize = 7.6,
+                FontSize = 9,
                 Foreground = (TryFindResource("SecondaryText") as Brush ?? Brushes.Gray)
             },
             Background = Brushes.Transparent,
@@ -3315,8 +3315,8 @@ public partial class ChatWindow : Window
             Cursor = Cursors.Hand,
             VerticalAlignment = VerticalAlignment.Center,
             Visibility = Visibility.Collapsed,
-            Width = 18,
-            Height = 18,
+            Width = 20,
+            Height = 20,
             Padding = new Thickness(0),
             Opacity = 0.72,
             ToolTip = _activeTab == "Cowork" ? "작업 유형" : "대화 주제 변경"