feat: add custom publish time and last updated time display

- Add custom publish time field to article create/edit forms
  - Support datetime-local input for manual time setting
  - Auto-set on first publish if left blank
  - Works for both admin and user article forms

- Display last updated time on article detail page
  - Show both published time and last updated time
  - Auto-maintained by GORM on each update
  - Format: YYYY-MM-DD HH:MM

- Add i18n support for new fields
  - article_published_at: Published Time / 发布时间
  - article_published_at_hint: Leave blank to auto-set on publish / 留空则在发布时自动设置
  - article_last_updated: Last Updated / 最后更新

- Update handlers and templates
  - handlers/article.go: Add parsePublishedAt/formatPublishedAt functions
  - handlers/home.go: Add formatUpdateTime function
  - handlers/my_articles.go: Support custom publish time in user articles
  - templates: Add datetime-local inputs and time display

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

handlers/my_articles.go

@@ -66,16 +66,17 @@ func MyArticleEditPage(db *gorm.DB) gin.HandlerFunc {
 		}
 
 		renderMyArticleForm(c, db, articleForm{
-			Title:     article.Title,
-			Slug:      article.Slug,
-			Summary:   article.Summary,
-			Content:   article.Content,
-			Cover:     article.Cover,
-			StatusStr: strconv.Itoa(article.Status),
-			IsTop:     article.IsTop,
-			Action:    "/my/articles/" + id + "/edit",
-			TitleText: tr["article_edit_title"],
-			ArticleID: article.ID,
+			Title:       article.Title,
+			Slug:        article.Slug,
+			Summary:     article.Summary,
+			Content:     article.Content,
+			Cover:       article.Cover,
+			StatusStr:   strconv.Itoa(article.Status),
+			IsTop:       article.IsTop,
+			PublishedAt: formatPublishedAt(article.PublishedAt),
+			Action:      "/my/articles/" + id + "/edit",
+			TitleText:   tr["article_edit_title"],
+			ArticleID:   article.ID,
 		}, "")
 	}
 }
@@ -117,12 +118,19 @@ func MyArticleUpdate(db *gorm.DB) gin.HandlerFunc {
 
 		newStatus := statusFromForm(f.StatusStr)
 
-		// Stamp the publish time the first time an article is published.
-		wasPublished := article.Status == models.ArticlePublished
-		var publishedAt *time.Time = article.PublishedAt
-		if newStatus == models.ArticlePublished && !wasPublished && publishedAt == nil {
-			now := time.Now()
-			publishedAt = &now
+		// Handle published_at: use form value if provided, otherwise auto-stamp on first publish.
+		var publishedAt *time.Time
+		if f.PublishedAt != "" {
+			// User provided a custom published time
+			publishedAt = parsePublishedAt(f.PublishedAt)
+		} else {
+			// Stamp the publish time the first time an article is published.
+			wasPublished := article.Status == models.ArticlePublished
+			publishedAt = article.PublishedAt
+			if newStatus == models.ArticlePublished && !wasPublished && publishedAt == nil {
+				now := time.Now()
+				publishedAt = &now
+			}
 		}
 
 		updates := map[string]interface{}{