refactor(chat): simplify code and improve readability

- Remove redundant null check in `selectAgent` method.
- Use direct property assignment for icons in `AutoDevInputSection`.
- Clean up button initialization by removing unnecessary line breaks.

Author: phodal

core/src/main/kotlin/cc/unitmesh/devti/gui/chat/AutoDevInput.kt

@@ -64,7 +64,6 @@ class AutoDevInput(
             object : AnAction() {
                 override fun actionPerformed(actionEvent: AnActionEvent) {
                     val editor = editor ?: return
-
                     // Insert a new line
                     CommandProcessor.getInstance().executeCommand(project, {
                         val eol = "\n"

core/src/main/kotlin/cc/unitmesh/devti/gui/chat/AutoDevInputSection.kt

@@ -86,11 +86,11 @@ class AutoDevInputSection(private val project: Project, val disposable: Disposab
 
     init {
         val sendButtonPresentation = Presentation(AutoDevBundle.message("chat.panel.send"))
-        sendButtonPresentation.setIcon(AutoDevIcons.Send)
+        sendButtonPresentation.icon = AutoDevIcons.Send
         this.sendButtonPresentation = sendButtonPresentation
 
         val stopButtonPresentation = Presentation("Stop")
-        stopButtonPresentation.setIcon(AutoDevIcons.Stop)
+        stopButtonPresentation.icon = AutoDevIcons.Stop
         this.stopButtonPresentation = stopButtonPresentation
 
         sendButton = ActionButton(
@@ -101,9 +101,7 @@ class AutoDevInputSection(private val project: Project, val disposable: Disposab
                     }
                 }.actionPerformed(it)
             },
-            this.sendButtonPresentation,
-            "",
-            Dimension(20, 20)
+            this.sendButtonPresentation, "", Dimension(20, 20)
         )
 
         stopButton = ActionButton(
@@ -114,9 +112,7 @@ class AutoDevInputSection(private val project: Project, val disposable: Disposab
                     }
                 }.actionPerformed(it)
             },
-            this.stopButtonPresentation,
-            "",
-            Dimension(20, 20)
+            this.stopButtonPresentation, "", Dimension(20, 20)
         )
 
         input = AutoDevInput(project, listOf(), disposable, this)

core/src/main/kotlin/cc/unitmesh/devti/gui/chat/ChatCodingPanel.kt

@@ -302,9 +302,7 @@ class ChatCodingPanel(private val chatCodingService: ChatCodingService, val disp
     }
 
     fun selectAgent(config: CustomAgentConfig) {
-        inputSection.let {
-            it?.selectAgent(config)
-        }
+        inputSection.selectAgent(config)
     }
 
     fun appendWebView(content: String, project: Project) {