AX Agent 메시지 메타 가독성과 끝단 정렬 보정

- 사용자와 assistant 메시지 행 여백을 줄여 transcript 좌우 끝단 정렬감을 높였습니다.
- AX 에이전트 라벨, 아이콘, 시간 표기 글꼴 크기와 대비를 키워 메타 정보 가독성을 보강했습니다.
- 관련 변경 이력을 README와 DEVELOPMENT 문서에 반영했습니다.

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

src/AxCopilot/Views/ChatWindow.xaml.cs

@@ -4409,7 +4409,7 @@ public partial class ChatWindow : Window
             {
                 HorizontalAlignment = HorizontalAlignment.Right,
                 MaxWidth = GetMessageMaxWidth(),
-                Margin = new Thickness(240, 3, 10, 3),
+                Margin = new Thickness(132, 4, 4, 6),
             };
 
             var bubble = new Border
@@ -4454,11 +4454,11 @@ public partial class ChatWindow : Window
             userBottomBar.Children.Add(new TextBlock
             {
                 Text = timestamp.ToString("HH:mm"),
-                FontSize = 8, Opacity = 0.34,
+                FontSize = 10.5, Opacity = 0.52,
                 Foreground = TryFindResource("SecondaryText") as Brush ?? Brushes.Gray,
                 HorizontalAlignment = HorizontalAlignment.Right,
                 VerticalAlignment = VerticalAlignment.Center,
-                Margin = new Thickness(0, 0, 2, 0),
+                Margin = new Thickness(0, 0, 2, 1),
             });
             userBottomBar.Children.Add(userActionBar);
             wrapper.Children.Add(userBottomBar);
@@ -4492,7 +4492,7 @@ public partial class ChatWindow : Window
             {
                 HorizontalAlignment = HorizontalAlignment.Left,
                 MaxWidth = GetMessageMaxWidth(),
-                Margin = new Thickness(2, 4, 210, 4)
+                Margin = new Thickness(4, 6, 132, 6)
             };
             if (animate) ApplyMessageEntryAnimation(container);
 
@@ -4504,7 +4504,7 @@ public partial class ChatWindow : Window
             {
                 Text = "\uE945",
                 FontFamily = new FontFamily("Segoe MDL2 Assets"),
-                FontSize = 7.5,
+                FontSize = 10,
                 Foreground = secondaryText,
                 VerticalAlignment = VerticalAlignment.Center,
             };
@@ -4513,8 +4513,8 @@ public partial class ChatWindow : Window
             headerSp.Children.Add(new TextBlock
             {
                 Text = agentName,
-                FontSize = 8.5,
-                FontWeight = FontWeights.Medium,
+                FontSize = 11.5,
+                FontWeight = FontWeights.SemiBold,
                 Foreground = secondaryText,
                 Margin = new Thickness(4, 0, 0, 0),
                 VerticalAlignment = VerticalAlignment.Center,
@@ -4676,10 +4676,10 @@ public partial class ChatWindow : Window
             actionBar.Children.Add(new TextBlock
             {
                 Text = aiTimestamp.ToString("HH:mm"),
-                FontSize = 8, Opacity = 0.34,
+                FontSize = 10.5, Opacity = 0.52,
                 Foreground = btnColor,
                 VerticalAlignment = VerticalAlignment.Center,
-                Margin = new Thickness(3, 0, 0, 0),
+                Margin = new Thickness(4, 0, 0, 1),
             });
 
             container.Children.Add(actionBar);