refactor(devti): enhance UI styling and theme support

- Update Markdown viewer background color to match current theme
- Improve Plan toolbar appearance and spacing
- Adjust TaskStepPanel label styling for better readability
- Update AI copilot icon color to match new branding
- Enlarge stop icon for better visibility

Author: phodal

core/src/main/kotlin/cc/unitmesh/devti/sketch/ui/code/MarkdownWebViewer.kt

@@ -5,6 +5,7 @@ import com.intellij.openapi.util.text.StringUtil
 import com.intellij.ui.BrowserHyperlinkListener
 import com.intellij.ui.ColorUtil
 import com.intellij.util.ui.HTMLEditorKitBuilder
+import com.intellij.util.ui.JBUI
 import com.intellij.util.ui.UIUtil
 import javax.swing.JEditorPane
 import javax.swing.text.DefaultCaret
@@ -15,8 +16,8 @@ object MarkdownWebViewer {
         jEditorPane.setContentType("text/html")
         val htmlEditorKit = HTMLEditorKitBuilder().build()
 
-        val backgroundColor = UIUtil.getPanelBackground()
-        val backgroundColorHex = ColorUtil.toHex(backgroundColor)
+        val backgroundColor = JBUI.CurrentTheme.ToolWindow.background()
+        val bg = ColorUtil.toHex(backgroundColor)
 
         val editorFontName = EditorColorsManager.getInstance().schemeForCurrentUITheme.editorFontName
         val editorFontSize = EditorColorsManager.getInstance().schemeForCurrentUITheme.editorFontSize
@@ -31,8 +32,8 @@ object MarkdownWebViewer {
             h3 { font-size: 1.2em; font-weight: bold; }
             h4, h5, h6 { font-size: 1.1em; font-weight: bold; }
             
-            pre { background-color: #f5f5f5; border-radius: 4px; padding: 8px; overflow-x: auto; margin: 1em 0; }
-            code { font-family: 'JetBrains Mono', Consolas, monospace; background-color: #f5f5f5; padding: 2px 4px; border-radius: 3px; font-size: 0.9em; }
+            pre { background-color: #$bg; border-radius: 4px; padding: 8px; overflow-x: auto; margin: 1em 0; }
+            code { font-family: 'JetBrains Mono', Consolas, monospace; background-color: #$bg; padding: 2px 4px; border-radius: 3px; font-size: 0.9em; }
             
             /* Lists */
             ul, ol { margin-top: 0.5em; margin-bottom: 0.5em; padding-left: 2em; }
@@ -51,7 +52,7 @@ object MarkdownWebViewer {
             a:hover { text-decoration: underline; }
             
             /* Horizontal rule */
-            hr { border: 0; height: 1px; background-color: #ddd; margin: 1em 0; }
+            hr { border: 0; height: 1px; background-color: #$bg; margin: 1em 0; }
             
             /* Inline elements */
             strong, b { font-weight: bold; }

core/src/main/kotlin/cc/unitmesh/devti/sketch/ui/plan/PlanToolbarFactory.kt

@@ -30,17 +30,22 @@ class PlanToolbarFactory(private val project: Project) {
                 this.targetComponent = component
             }
 
-        val titleLabel = JLabel("Thought Plan").apply {
+        val bg = JBUI.CurrentTheme.ToolWindow.background()
+        toolbar.component.setBackground(bg)
+
+        val titleLabel = JLabel("Plan").apply {
             border = JBUI.Borders.empty(0, 10)
         }
 
         val toolbarPanel = JPanel(BorderLayout()).apply {
             add(titleLabel, BorderLayout.WEST)
             add(toolbar.component, BorderLayout.EAST)
+        }.also {
+            it.background = bg
         }
 
         val toolbarWrapper = Wrapper(JBUI.Panels.simplePanel(toolbarPanel)).also {
-            it.border = JBUI.Borders.customLine(UIUtil.getBoundsColor(), 1, 1, 1, 1)
+            it.border = JBUI.Borders.customLine(UIUtil.getBoundsColor(), 0, 0, 1, 0)
         }
 
         return toolbarWrapper

core/src/main/kotlin/cc/unitmesh/devti/sketch/ui/plan/TaskStepPanel.kt

@@ -95,10 +95,9 @@ class TaskStepPanel(
     private fun createStyledTaskLabel(): JEditorPane {
         val labelText = getLabelTextByStatus()
 
-        val backgroundColor = UIUtil.getPanelBackground()
+        val backgroundColor = JBUI.CurrentTheme.ToolWindow.background()
         val backgroundColorHex = ColorUtil.toHex(backgroundColor)
 
-        // Get the foreground color that matches the current theme
         val foregroundColor = UIUtil.getLabelForeground()
         val foregroundColorHex = ColorUtil.toHex(foregroundColor)