依据 SECURITY_SEO_AUDIT.md 实施第一轮安全/SEO/GEO 修复

代码改动：
- SEO-02 产品页标题品牌重复：Product::seoTitle() 去掉品牌后缀，由视图统一追加 $siteName
- SEO-05/Geo-03 结构化数据：布局增 WebSite+SearchAction；产品页 Product+BreadcrumbList；文章页 Article+BreadcrumbList（含作者/发布日期）
- SEO-06 hreflang 自引用（zh-CN/x-default）
- SEC-02 新增 public/.well-known/security.txt
- GEO-05 新增 public/llms.txt

记录文档（供未来开发者接手）：
- CHANGELOG.md：版本与变更日志
- docs/SECURITY_SEO_REMEDIATION.md：逐项状态总表 + 改动位置 + 上线 curl 自检清单
（SEC-01/REL-01~03/PHY-01~04 等需 Tailwind 构建或云端操作项标记为待办，未自动改以免破坏站点）

resources/views/articles/show.blade.php

@@ -48,6 +48,37 @@
             @endif
         </article>
 
+        @php
+            // 结构化数据：Article + BreadcrumbList（审计 SEO-05 / GEO-03 作者与发布信号）
+            $logoUrl = '/images/logo-dark.png';
+            $articleSchema = [
+                '@context' => 'https://schema.org',
+                '@type' => 'Article',
+                'headline' => $article->title,
+                'description' => $article->seoDescription(),
+                'author' => ['@type' => 'Organization', 'name' => $siteName],
+                'publisher' => [
+                    '@type' => 'Organization',
+                    'name' => $siteName,
+                    'logo' => ['@type' => 'ImageObject', 'url' => asset($logoUrl)],
+                ],
+                'datePublished' => $article->published_at?->toIso8601String(),
+                'dateModified' => $article->updated_at?->toIso8601String(),
+                'mainEntityOfPage' => ['@type' => 'WebPage', '@id' => url()->current()],
+            ];
+            $breadcrumbSchema = [
+                '@context' => 'https://schema.org',
+                '@type' => 'BreadcrumbList',
+                'itemListElement' => [
+                    ['@type' => 'ListItem', 'position' => 1, 'name' => '首页', 'item' => url('/')],
+                    ['@type' => 'ListItem', 'position' => 2, 'name' => '技术文章', 'item' => route('articles.index')],
+                    ['@type' => 'ListItem', 'position' => 3, 'name' => $article->title, 'item' => url()->current()],
+                ],
+            ];
+        @endphp
+        <script type="application/ld+json">{!! json_encode($articleSchema, JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES | JSON_HEX_TAG) !!}</script>
+        <script type="application/ld+json">{!! json_encode($breadcrumbSchema, JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES | JSON_HEX_TAG) !!}</script>
+
         <div class="mt-6">
             <a href="{{ route('articles.index') }}" class="inline-flex items-center gap-1.5 text-sm font-medium text-primary hover:text-primary-hover">
                 <x-icon name="arrow" :size="16" class="rotate-180" /> 返回文章列表