fix: 修复帖子提交审核权限缺失 + 防重复提交 + 分页逻辑复用

- 修复 Submit API 缺少 uid 权限检查，任意登录用户可提交他人帖子审核
- 前端 handleSubmit 添加 submitting 锁和按钮禁用/恢复，防止重复提交
- 分页计算 TotalPages/PrevPage/NextPage 提取为 Pagination 方法，消除三处重复代码

internal/controller/admin/admin_post_controller.go

@@ -43,11 +43,7 @@ func (ctrl *AdminPostController) PostsPage(c *gin.Context) {
 
 	p := common.Pagination{Page: page, PageSize: pageSize}
 	p.DefaultPagination()
-	totalPages := int((total + int64(p.PageSize) - 1) / int64(p.PageSize))
-	prevPage := p.Page - 1
-	if prevPage < 1 { prevPage = 1 }
-	nextPage := p.Page + 1
-	if nextPage > totalPages { nextPage = totalPages }
+	totalPages := p.TotalPages(total)
 
 	c.HTML(http.StatusOK, "admin/posts/index.html", common.BuildAdminPageData(c, gin.H{
 		"Title":       "内容管理",
@@ -55,8 +51,8 @@ func (ctrl *AdminPostController) PostsPage(c *gin.Context) {
 		"Total":       total,
 		"Page":        p.Page,
 		"TotalPages":  totalPages,
-		"PrevPage":    prevPage,
-		"NextPage":    nextPage,
+		"PrevPage":    p.PrevPage(),
+		"NextPage":    p.NextPage(totalPages),
 		"Keyword":     keyword,
 		"Status":      status,
 		"StatusNames": model.PostStatusDisplayNames,