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>

templates/pages/home.html

@@ -1,5 +1,21 @@
 {{define "home"}}
 {{template "header" .}}
+
+<!-- Search Box -->
+<section class="max-w-5xl mx-auto px-4 py-6">
+    <div class="flex justify-center">
+        <form action="/search" method="get" class="w-full max-w-2xl">
+            <div class="relative">
+                <input type="text" name="q" placeholder="{{index .Tr "search_placeholder"}}"
+                    class="w-full px-4 py-3 pl-12 border border-gray-300 rounded-lg focus:ring-2 focus:ring-blue-500 focus:border-blue-500 outline-none transition-colors">
+                <svg class="absolute left-4 top-1/2 transform -translate-y-1/2 w-5 h-5 text-gray-400" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                    <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M21 21l-6-6m2-5a7 7 0 11-14 0 7 7 0 0114 0z"/>
+                </svg>
+            </div>
+        </form>
+    </div>
+</section>
+
 <section class="max-w-5xl mx-auto px-4 py-20 text-center">
     <h1 class="text-5xl font-extrabold text-gray-900 mb-4 flex items-center justify-center gap-3">
         <svg class="w-12 h-12 text-blue-600" fill="none" stroke="currentColor" viewBox="0 0 24 24">
@@ -15,11 +31,24 @@
     </p>
 </section>
 
-<section class="max-w-4xl mx-auto px-4 py-8">
-    <h2 class="text-3xl font-bold text-gray-900 mb-8 text-center">{{index .Tr "home_latest"}}</h2>
+<section class="max-w-7xl mx-auto px-4 py-8">
+    <div class="flex gap-8">
+        <!-- Main content (articles) -->
+        <div class="flex-1">
+            {{if .FilterTag}}
+            <div class="mb-6 flex items-center gap-2 text-sm">
+                <span class="text-gray-600">{{index .Tr "tag_filter"}}:</span>
+                <span class="px-3 py-1 bg-blue-100 text-blue-700 rounded-full">
+                    {{if eq .Lang "zh"}}{{.FilterTag.NameZh}}{{else}}{{.FilterTag.NameEn}}{{end}}
+                </span>
+                <a href="/" class="text-blue-600 hover:text-blue-800">{{index .Tr "tag_all"}}</a>
+            </div>
+            {{end}}
 
-    <!-- Articles Container -->
-    <div id="articlesContainer" class="space-y-6">
+            <h2 class="text-3xl font-bold text-gray-900 mb-8 text-center">{{index .Tr "home_latest"}}</h2>
+
+            <!-- Articles Container -->
+            <div id="articlesContainer" class="space-y-6">
         {{range .Articles}}
         <article class="article-card bg-white rounded-xl shadow-sm border border-gray-200 overflow-hidden hover:shadow-md transition-shadow" data-cover="{{.Cover}}">
             <a href="/article/{{.Slug}}" class="block article-link">
@@ -39,6 +68,15 @@
                         {{if .Summary}}
                         <p class="text-gray-500 text-sm line-clamp-3 mb-3">{{.Summary}}</p>
                         {{end}}
+                        {{if .Tags}}
+                        <div class="flex items-center gap-2 flex-wrap mb-3">
+                            {{range .Tags}}
+                            <a href="/?tag={{.Slug}}" class="text-xs px-2 py-1 bg-gray-100 hover:bg-blue-100 text-gray-600 hover:text-blue-600 rounded transition-colors">
+                                {{if eq $.Lang "zh"}}{{.NameZh}}{{else}}{{.NameEn}}{{end}}
+                            </a>
+                            {{end}}
+                        </div>
+                        {{end}}
                         <div class="flex items-center justify-between">
                             <span class="text-sm text-blue-600 font-medium">{{index $.Tr "home_read_more"}} →</span>
                             <div class="flex items-center gap-4 text-sm text-gray-500">
@@ -76,6 +114,28 @@
     <div id="noMoreArticles" class="hidden text-center text-gray-500 py-8">
         {{if eq .Lang "zh"}}没有更多文章了{{else}}No more articles{{end}}
     </div>
+        </div>
+
+        <!-- Sidebar (tags) -->
+        <aside class="w-72 flex-shrink-0 hidden lg:block">
+            <div class="sticky top-6">
+                <h3 class="text-lg font-bold text-gray-900 mb-4">{{index .Tr "tags_title"}}</h3>
+                {{if .Tags}}
+                <div class="flex flex-wrap gap-2">
+                    {{range .Tags}}
+                    <a href="/?tag={{.Slug}}"
+                        class="px-3 py-1 text-sm bg-gray-100 hover:bg-blue-100 text-gray-700 hover:text-blue-700 rounded-full transition-colors inline-flex items-center gap-1">
+                        <span>{{if eq $.Lang "zh"}}{{.NameZh}}{{else}}{{.NameEn}}{{end}}</span>
+                        <span class="text-xs text-gray-500">({{.Count}})</span>
+                    </a>
+                    {{end}}
+                </div>
+                {{else}}
+                <p class="text-sm text-gray-500">{{if eq .Lang "zh"}}暂无标签{{else}}No tags yet{{end}}</p>
+                {{end}}
+            </div>
+        </aside>
+    </div>
 </section>
 
 <style>