refactor(gui): improve UI consistency and appearance #352

- Replace plain JPanel with JBUI.Panels.simplePanel for contentPanel in AutoDevPlannerToolWindow
- Enhance buttonPanel in EditPlanViewPanel and IssueInputViewPanel with background color matching the editor's background

Author: phodal

core/src/main/kotlin/cc/unitmesh/devti/gui/planner/AutoDevPlannerToolWindow.kt

@@ -18,6 +18,7 @@ import com.intellij.openapi.ui.SimpleToolWindowPanel
 import com.intellij.openapi.vcs.changes.Change
 import com.intellij.openapi.wm.ToolWindowManager
 import com.intellij.ui.dsl.builder.panel
+import com.intellij.util.ui.JBUI
 import java.awt.*
 import javax.swing.*
 
@@ -29,7 +30,7 @@ class AutoDevPlannerToolWindow(val project: Project) : SimpleToolWindowPanel(tru
         PlanLangSketch(project, content, MarkdownPlanParser.parse(content).toMutableList(), true)
 
     private var markdownEditor: MarkdownLanguageField? = null
-    private val contentPanel = JPanel(BorderLayout())
+    private val contentPanel = JBUI.Panels.simplePanel()
 
     private var currentView: PlannerView? = null
     private var currentCallback: ((String) -> Unit)? = null

core/src/main/kotlin/cc/unitmesh/devti/gui/planner/EditPlanViewPanel.kt

@@ -18,8 +18,11 @@ class EditPlanViewPanel(
 
     init {
         markdownEditor = MarkdownLanguageField(project, content, "Edit your plan here...", "plan.md")
-        
-        val buttonPanel = JPanel(BorderLayout())
+
+        val buttonPanel = JPanel(BorderLayout()).apply {
+            background = markdownEditor?.getEditor(true)?.backgroundColor
+        }
+
         val buttonsBox = Box.createHorizontalBox().apply {
             add(JButton("Save").apply {
                 addActionListener {

core/src/main/kotlin/cc/unitmesh/devti/shadow/IssueInputViewPanel.kt

@@ -24,7 +24,10 @@ class IssueInputViewPanel(
     init {
         textArea = MarkdownLanguageField(project, "", "Enter Issue Description", "issue.md")
 
-        val buttonPanel = JPanel(BorderLayout())
+        val buttonPanel = JPanel(BorderLayout()).apply {
+            background = textArea?.getEditor(true)?.backgroundColor
+        }
+
         val buttonsBox = Box.createHorizontalBox().apply {
             add(JButton("Submit").apply {
                 addActionListener {