feat: add article management (list, edit, delete)

- Add admin article list page at /admin/articles with status badges,
  pin marker, publish time, and edit/delete actions
- Share the create/edit form: dynamic action URL, prefilled fields,
  is_top checkbox state, and create-vs-edit heading
- Add ArticleUpdate/ArticleDelete handlers (soft-delete via DeletedAt);
  stamp PublishedAt on first publish
- Add "Manage Articles" entry on the dashboard
- Hide home page sign-in/dashboard buttons
- Add EN/ZH i18n keys for the management UI

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

i18n/i18n.go

@@ -118,6 +118,21 @@ var translations = map[Lang]map[string]string{
 		"article_content_required": "Content is required.",
 		"article_back_home":      "Back to Home",
 		"article_not_found":      "Article not found.",
+
+		// Article management
+		"article_list_title":      "Articles",
+		"article_edit_title":      "Edit Article",
+		"article_manage":          "Manage Articles",
+		"article_edit":            "Edit",
+		"article_delete":          "Delete",
+		"article_delete_confirm":  "Delete this article?",
+		"article_updated":         "Article updated.",
+		"article_deleted":         "Article deleted.",
+		"article_archived":        "Archived",
+		"article_col_title":       "Title",
+		"article_col_status":      "Status",
+		"article_col_published":   "Published",
+		"article_col_actions":     "Actions",
 	},
 	ZH: {
 		// 导航
@@ -221,6 +236,21 @@ var translations = map[Lang]map[string]string{
 		"article_content_required": "正文不能为空。",
 		"article_back_home":      "返回首页",
 		"article_not_found":      "文章不存在。",
+
+		// 文章管理
+		"article_list_title":      "文章管理",
+		"article_edit_title":      "编辑文章",
+		"article_manage":          "文章管理",
+		"article_edit":            "编辑",
+		"article_delete":          "删除",
+		"article_delete_confirm":  "确认删除这篇文章？",
+		"article_updated":         "文章已更新。",
+		"article_deleted":         "文章已删除。",
+		"article_archived":        "已归档",
+		"article_col_title":       "标题",
+		"article_col_status":      "状态",
+		"article_col_published":   "发布时间",
+		"article_col_actions":     "操作",
 	},
 }