feat: set Gateway 3 as root index and move dispatches to /dispatches/

- Update src/index.njk with Gateway 3 homelab services router and cluster telemetry
- Create src/dispatches.njk for the full-width technical dispatches feed and tag filters
- Update src/_data/site.json navigation hierarchy to reflect root Gateway and /dispatches/
- Update breadcrumbs and return links in post.njk and hero-tile.njk

src/_includes/layouts/post.njk

@@ -52,7 +52,7 @@
       </div>
 
       <div style="padding-top: 10px; border-top: var(--border-width) solid var(--border-color);">
-        <a href="/" class="filter-tag-btn" style="width: 100%; justify-content: center;">
+        <a href="/dispatches/" class="filter-tag-btn" style="width: 100%; justify-content: center;">
           &larr; Return to Dispatches
         </a>
       </div>
@@ -63,7 +63,7 @@
   <article class="article-tile" aria-labelledby="article-title">
     <header class="article-header-block">
       <nav class="article-breadcrumbs" aria-label="Breadcrumb">
-        <a href="/">~/NOTES</a>
+        <a href="/dispatches/">~/NOTES</a>
         <span>/</span>
         <span>{{ (tags | filterTagList)[0] | default('DISPATCHES') | upper }}</span>
         <span>/</span>