feat(vcs): add notification for empty diff context

Add a notification to inform the user when the diff context is empty or cannot provide enough useful information. This helps improve user experience and provides feedback on the status of the diff context.

src/main/kotlin/cc/unitmesh/devti/actions/vcs/CommitMessageSuggestionAction.kt

@@ -1,5 +1,6 @@
 package cc.unitmesh.devti.actions.vcs
 
+import cc.unitmesh.devti.AutoDevNotifications
 import cc.unitmesh.devti.actions.chat.base.ChatBaseAction
 import cc.unitmesh.devti.gui.chat.ChatActionType
 import cc.unitmesh.devti.llms.LlmFactory
@@ -35,6 +36,7 @@ class CommitMessageSuggestionAction : ChatBaseAction() {
         val diffContext = project.service<VcsPrompting>().prepareContext()
         if (diffContext.isEmpty() || diffContext == "\n") {
             logger.warn("Diff context is empty or cannot get enough useful context.")
+            AutoDevNotifications.notify(project, "Diff context is empty or cannot get enough useful context.")
             return
         }