feat: add admin publishing workflow and yar theme

Add Go/Postgres admin APIs, Angular admin UI, manual build flow, asset uploads, markdown import/export, configurable slug generation, and the Yar reading theme. Exclude local docs and generated development artifacts from version control.

frontend/site/src/components/DefaultPost.astro

@@ -0,0 +1,130 @@
+---
+import SiteNav from './SiteNav.astro';
+import { site } from '../lib/siteConfig';
+import { tagSlug } from '../lib/posts';
+
+type Props = {
+  post: any;
+};
+
+const { post } = Astro.props;
+const { Content } = post;
+const title = post.frontmatter.title;
+const date = post.frontmatter.created_at ?? post.frontmatter.published_at ?? post.frontmatter.updated_at;
+---
+
+<main class="page article-page">
+  <SiteNav />
+
+  <article class="article">
+    <header>
+      <h1>{title}</h1>
+      {date && (
+        <time datetime={date}>
+          {new Date(date).toLocaleDateString(site.language)}
+        </time>
+      )}
+      {post.frontmatter.summary && <p class="summary">{post.frontmatter.summary}</p>}
+      {post.frontmatter.tags?.length > 0 && (
+        <ul class="tags article-tags" aria-label="Tags">
+          {post.frontmatter.tags.map((tag) => (
+            <li>
+              <a href={`/tags/${tagSlug(tag)}/`}>{tag}</a>
+            </li>
+          ))}
+        </ul>
+      )}
+    </header>
+
+    <Content />
+  </article>
+</main>
+
+<style>
+  .page {
+    width: min(860px, calc(100% - 32px));
+    margin: 0 auto;
+    padding: 56px 0 80px;
+    color: #20201d;
+    font-family:
+      Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI",
+      sans-serif;
+  }
+
+  .page :global(.site-nav) {
+    display: flex;
+    flex-wrap: wrap;
+    gap: 8px 18px;
+    margin-bottom: 36px;
+    color: #625a50;
+    font-size: 0.95rem;
+  }
+
+  .page :global(.site-nav a),
+  .tags a {
+    color: inherit;
+    text-decoration: none;
+  }
+
+  .page :global(.site-nav a:hover) {
+    text-decoration: underline;
+    text-underline-offset: 4px;
+  }
+
+  .article {
+    line-height: 1.8;
+  }
+
+  .article header {
+    border-bottom: 1px solid #d8d1c3;
+    margin-bottom: 32px;
+    padding-bottom: 24px;
+  }
+
+  .article h1 {
+    margin: 0 0 16px;
+    font-size: clamp(2.1rem, 7vw, 4rem);
+  }
+
+  .summary {
+    color: #5b554d;
+  }
+
+  time {
+    color: #7a7268;
+    font-size: 0.9rem;
+  }
+
+  .tags {
+    display: flex;
+    flex-wrap: wrap;
+    gap: 6px;
+    padding: 0;
+    margin: 16px 0 0;
+    list-style: none;
+  }
+
+  .tags li {
+    border: 1px solid #d0c8bb;
+    border-radius: 999px;
+    color: #5f584d;
+    font-size: 0.82rem;
+  }
+
+  .tags a {
+    display: inline-block;
+    padding: 2px 8px;
+  }
+
+  .article :global(pre) {
+    overflow-x: auto;
+    border-radius: 8px;
+    padding: 16px;
+    background: #272822;
+    color: #f8f8f2;
+  }
+
+  .article :global(code) {
+    font-family: "SFMono-Regular", Consolas, "Liberation Mono", monospace;
+  }
+</style>