fix(post): prevent duplicate submission and fix navigation after posting

- add guard clause to prevent duplicate clicks when posting is in progress
- replace navigation.goBack() with navigation.reset to Main screen for cleaner navigation stack after post creation, update, and voting post submission

src/screens/create/CreatePostScreen.tsx

@@ -334,6 +334,9 @@ export const CreatePostScreen: React.FC<CreatePostScreenProps> = (props) => {
 
   // 发布帖子
   const handlePost = async () => {
+    // 防止重复点击
+    if (posting) return;
+
     if (!content.trim()) {
       Alert.alert('错误', '请输入帖子内容');
       return;
@@ -373,7 +376,10 @@ export const CreatePostScreen: React.FC<CreatePostScreenProps> = (props) => {
           message: '投票帖已提交，内容审核中，稍后展示',
           duration: 2600,
         });
-        navigation.goBack();
+        navigation.reset({
+          index: 0,
+          routes: [{ name: 'Main' }],
+        });
       } else {
         if (isEditMode && editPostID) {
           const updated = await postService.updatePost(editPostID, {
@@ -390,7 +396,10 @@ export const CreatePostScreen: React.FC<CreatePostScreenProps> = (props) => {
             message: '帖子内容已更新',
             duration: 2200,
           });
-          navigation.goBack();
+          navigation.reset({
+            index: 0,
+            routes: [{ name: 'Main' }],
+          });
         } else {
           // 创建普通帖子
           await postService.createPost({
@@ -404,7 +413,10 @@ export const CreatePostScreen: React.FC<CreatePostScreenProps> = (props) => {
             message: '帖子已提交，内容审核中，稍后展示',
             duration: 2600,
           });
-          navigation.goBack();
+          navigation.reset({
+            index: 0,
+            routes: [{ name: 'Main' }],
+          });
         }
       }
     } catch (error) {