blog: three curated series across the whole catalogue + badge on post pages

Extends the lone security thread into three arcs that read as skill pillars -
SECURITY (6), NETWORKING (5), PLATFORM (7) - so every post carries a numbered
badge and the catalogue advertises three areas of depth rather than a loose
list. Adds the badge to the post detail header too, styled to match the cards.

src/pages/blog/[slug].astro

@@ -2,6 +2,7 @@
 import Layout from "../../layouts/Layout.astro";
 import { getPosts, formatDate } from "../../lib/blog";
 import { readingTime } from "../../lib/reading";
+import { series } from "../../data/series";
 import { render } from "astro:content";
 import type { GetStaticPaths } from "astro";
 
@@ -21,6 +22,12 @@ const { Content } = await render(entry);
 
       <header class="post__head" data-reveal>
         <div class="post__meta mono">
+          {series[entry.id] && (
+            <>
+              <span class="post__series">{series[entry.id].name} · {String(series[entry.id].number).padStart(2, "0")}</span>
+              <span class="post__sep">·</span>
+            </>
+          )}
           <time datetime={entry.data.date.toISOString()}>{formatDate(entry.data.date)}</time>
           <span class="post__sep">·</span>
           <span>{readingTime(entry.body)}</span>
@@ -87,6 +94,16 @@ const { Content } = await render(entry);
     color: var(--text-faint);
     display: flex;
     gap: 0.5rem;
+    align-items: center;
+    flex-wrap: wrap;
+  }
+  .post__series {
+    color: var(--accent-2);
+    border: 1px solid var(--border-magenta);
+    border-radius: 3px;
+    padding: 2px 7px;
+    letter-spacing: 0.1em;
+    font-size: 0.66rem;
   }
   .post__sep {
     opacity: 0.6;