feat: implement tag management and search functionality

Features:
- Tag system with multi-language support (Chinese/English)
- Auto-create tags when associating with articles
- Tag filtering on homepage with visual indicators
- Full-text search across title, summary, and content
- Tag cloud sidebar showing article counts
- Search page with results display

Technical Implementation:
- Database models: Tag, ArticleTag (many-to-many)
- Tag count caching for performance
- Automatic tag slug generation
- Responsive design with mobile support
- I18n support for all new UI elements

Bug Fix:
- Fixed SQL column ambiguity error in tag filtering
- Added table prefix to ORDER BY clause in publishedArticleOrder

Routes:
- GET /search - Search results page
- GET /?tag=<slug> - Filter articles by tag
- GET /api/articles?tag=<slug> - API with tag filter support

Templates:
- Added tag input field to article create/edit form
- Added search box to homepage header
- Added tag cloud sidebar on homepage and search page
- Created new search results page template

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

handlers/home.go

@@ -3,6 +3,7 @@ package handlers
 import (
 	"fmt"
 	"net/http"
+	"strings"
 	"time"
 
 	"github.com/gin-contrib/sessions"
@@ -14,7 +15,7 @@ import (
 
 // publishedArticleOrder is the ordering used to list published articles:
 // pinned first, then by most recent publish/creation time.
-const publishedArticleOrder = "is_top DESC, published_at DESC, created_at DESC"
+const publishedArticleOrder = "articles.is_top DESC, articles.published_at DESC, articles.created_at DESC"
 
 // HomePage renders the public home page with the latest published articles.
 func HomePage(db *gorm.DB) gin.HandlerFunc {
@@ -23,12 +24,35 @@ func HomePage(db *gorm.DB) gin.HandlerFunc {
 		data := DefaultData(c)
 		data["Title"] = tr["page_home"]
 
+		// Get tag filter if present
+		tagSlug := c.Query("tag")
+
+		// Build query
+		query := db.Where("status = ?", models.ArticlePublished)
+
+		if tagSlug != "" {
+			// Join with article_tags to filter by tag
+			query = query.Joins("JOIN article_tags ON article_tags.article_id = articles.id").
+				Joins("JOIN tags ON tags.id = article_tags.tag_id").
+				Where("tags.slug = ?", tagSlug)
+
+			// Get tag info for display
+			var tag models.Tag
+			if err := db.Where("slug = ?", tagSlug).First(&tag).Error; err == nil {
+				data["FilterTag"] = tag
+			}
+		}
+
 		var articles []models.Article
-		db.Where("status = ?", models.ArticlePublished).
+		query.Preload("Tags").
 			Order(publishedArticleOrder).
 			Limit(10).
 			Find(&articles)
 
+		// Load all tags for sidebar
+		var tags []models.Tag
+		db.Where("count > 0").Order("count DESC, name_zh ASC").Find(&tags)
+
 		// Get comment counts for all articles
 		articleIDs := make([]uint, len(articles))
 		for i, article := range articles {
@@ -55,8 +79,9 @@ func HomePage(db *gorm.DB) gin.HandlerFunc {
 			commentCountMap[cc.ArticleID] = cc.Count
 		}
 
-		// Add comment counts to template data
+		// Add data to template
 		data["Articles"] = articles
+		data["Tags"] = tags
 		data["CommentCounts"] = commentCountMap
 
 		c.HTML(http.StatusOK, "home", data)
@@ -77,17 +102,33 @@ func HomeArticlesAPI(db *gorm.DB) gin.HandlerFunc {
 		pageSize := 10
 		offset := (page - 1) * pageSize
 
+		// Get tag filter if present
+		tagSlug := c.Query("tag")
+
+		// Build query
+		query := db.Where("status = ?", models.ArticlePublished)
+		countQuery := db.Model(&models.Article{}).Where("status = ?", models.ArticlePublished)
+
+		if tagSlug != "" {
+			// Join with article_tags to filter by tag
+			query = query.Joins("JOIN article_tags ON article_tags.article_id = articles.id").
+				Joins("JOIN tags ON tags.id = article_tags.tag_id").
+				Where("tags.slug = ?", tagSlug)
+
+			countQuery = countQuery.Joins("JOIN article_tags ON article_tags.article_id = articles.id").
+				Joins("JOIN tags ON tags.id = article_tags.tag_id").
+				Where("tags.slug = ?", tagSlug)
+		}
+
 		var articles []models.Article
-		db.Where("status = ?", models.ArticlePublished).
+		query.Preload("Tags").
 			Order(publishedArticleOrder).
 			Limit(pageSize).
 			Offset(offset).
 			Find(&articles)
 
 		var total int64
-		db.Model(&models.Article{}).
-			Where("status = ?", models.ArticlePublished).
-			Count(&total)
+		countQuery.Count(&total)
 
 		// Get comment counts for these articles
 		articleIDs := make([]uint, len(articles))
@@ -303,3 +344,68 @@ func recordArticleView(db *gorm.DB, articleID uint, c *gin.Context) {
 	db.Create(&view)
 	// Ignore errors - this is a best-effort tracking system
 }
+
+// SearchPage handles article search by keyword.
+func SearchPage(db *gorm.DB) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		tr := getTr(c)
+		data := DefaultData(c)
+
+		keyword := strings.TrimSpace(c.Query("q"))
+		data["SearchKeyword"] = keyword
+		data["Title"] = tr["search_title"]
+
+		if keyword == "" {
+			data["Articles"] = []models.Article{}
+			data["Tags"] = []models.Tag{}
+			data["CommentCounts"] = make(map[uint]int64)
+			c.HTML(http.StatusOK, "search", data)
+			return
+		}
+
+		// Search in title, summary, and content
+		searchPattern := "%" + keyword + "%"
+		var articles []models.Article
+		db.Where("status = ?", models.ArticlePublished).
+			Where("title LIKE ? OR summary LIKE ? OR content LIKE ?", searchPattern, searchPattern, searchPattern).
+			Preload("Tags").
+			Order(publishedArticleOrder).
+			Limit(50). // Limit search results
+			Find(&articles)
+
+		// Load all tags for sidebar
+		var tags []models.Tag
+		db.Where("count > 0").Order("count DESC, name_zh ASC").Find(&tags)
+
+		// Get comment counts
+		articleIDs := make([]uint, len(articles))
+		for i, article := range articles {
+			articleIDs[i] = article.ID
+		}
+
+		type CommentCount struct {
+			ArticleID uint
+			Count     int64
+		}
+		var commentCounts []CommentCount
+		if len(articleIDs) > 0 {
+			db.Model(&models.Comment{}).
+				Select("article_id, COUNT(*) as count").
+				Where("article_id IN ?", articleIDs).
+				Where("status = ?", models.CommentApproved).
+				Group("article_id").
+				Scan(&commentCounts)
+		}
+
+		commentCountMap := make(map[uint]int64)
+		for _, cc := range commentCounts {
+			commentCountMap[cc.ArticleID] = cc.Count
+		}
+
+		data["Articles"] = articles
+		data["Tags"] = tags
+		data["CommentCounts"] = commentCountMap
+
+		c.HTML(http.StatusOK, "search", data)
+	}
+}