feat(hero): use the workstation-to-server-racks render as the hero banner

Replaces the generated isometric diagram with the supplied 2752x1536
render (engineer at a multi-monitor desk, container streams flowing into
server racks). Re-exported at 1024/1280/2048 widths; alt text and the
lightbox caption now describe what the image actually shows.

src/pages/index.astro

@@ -77,7 +77,7 @@ const featuredMetrics: Record<string, string> = {
           <img
             class="hero-banner-img"
             src="/images/hero-banner.jpg"
-            alt="From Code to Production — Systems Architecture & DevOps Infrastructure Ecosystem"
+            alt="From Code to Production — engineer at a multi-monitor workstation, container streams flowing into server racks"
             width="1024"
             height="572"
             loading="eager"
@@ -125,13 +125,13 @@ const featuredMetrics: Record<string, string> = {
       <button type="button" class="arch-lightbox-close" aria-label="Close" onclick="this.closest('dialog').close()">&times;</button>
       <img
         src="/images/hero-banner-2x.webp"
-        alt="From Code to Production — Systems Architecture & DevOps Infrastructure Ecosystem"
+        alt="From Code to Production — engineer at a multi-monitor workstation, container streams flowing into server racks"
         width="2048"
         height="1144"
         loading="lazy"
       />
       <div class="arch-lightbox-caption">
-        <span>From Code to Production — Systems Architecture &amp; DevOps Infrastructure</span>
+        <span>From Code to Production — Workstation to Server Racks</span>
         <span class="arch-lightbox-hint">ESC / Click outside to close</span>
       </div>
     </div>

src/pages/zh/index.astro

@@ -78,7 +78,7 @@ const featuredMetrics: Record<string, string> = {
           <img
             class="hero-banner-img"
             src="/images/hero-banner.jpg"
-            alt="从代码到生产环境 —— 系统架构与 DevOps 运维生态图"
+            alt="从代码到生产环境 —— 工程师在多屏工作站前，容器数据流汇入机架服务器"
             width="1024"
             height="572"
             loading="eager"
@@ -126,13 +126,13 @@ const featuredMetrics: Record<string, string> = {
       <button type="button" class="arch-lightbox-close" aria-label="关闭" onclick="this.closest('dialog').close()">&times;</button>
       <img
         src="/images/hero-banner-2x.webp"
-        alt="从代码到生产环境 —— 系统架构与 DevOps 运维生态图"
+        alt="从代码到生产环境 —— 工程师在多屏工作站前，容器数据流汇入机架服务器"
         width="2048"
         height="1144"
         loading="lazy"
       />
       <div class="arch-lightbox-caption">
-        <span>从代码到生产环境 —— 系统架构与 DevOps 运维生态图</span>
+        <span>从代码到生产环境 —— 工程师在多屏工作站前，容器数据流汇入机架服务器</span>
         <span class="arch-lightbox-hint">ESC / 点击外部关闭</span>
       </div>
     </div>