blog: heroes belong in frontmatter - fix the five new posts

The five carried the hero only as an inline markdown image, but the index
cards and the post hero figure render from hero/heroAlt frontmatter - so
the cards showed no image and the post pages lost the hero treatment.
Moved each hero into frontmatter and dropped the inline line (the body
keeps only the diagram), matching every earlier post.

src/content/blog/sleep-half-the-fleet.md

@@ -4,10 +4,10 @@ date: 2026-08-02
 summary: "Three of this fleet's six machines were upgraded, verified healthy, and then deliberately shut down the same night — and the books record a state, not a failure. When a node's entire existence is a rebuildable document, powered off becomes something you schedule, not something you fear."
 tags: ["homelab", "operations", "talos", "sustainability", "architecture"]
 draft: false
+hero: "/blog/sleep-half-the-fleet.webp"
+heroAlt: "A dark tower of circuit-traced architecture at night — most windows unlit and resting, a few glowing where the core still works"
 ---
 
-![A dark tower of circuit-traced architecture at night — most windows unlit and resting, a few glowing where the core still works](/blog/sleep-half-the-fleet.webp)
-
 Homelabs run 24/7 out of habit. The habit comes with a scoreboard — `uptime` counters climbing into the
 hundreds of days, worn as proof of seriousness — and with two feelings nobody says out loud: the guilt of
 turning a server off, as if a dark machine means you weren't serious; and the quieter fear that if you do