dashboard: surface the hive's hyperhive rev on the H0M3 start page

Adds hyperhive_rev to the dashboard's /api/state StateSnapshot,
resolved via the same current_flake_rev helper get_agent_meta's
per-agent hyperhive_rev already uses. home.js renders it next to the
existing hive-identity line, truncated to the last 12 chars with the
full value in title=, hidden when the flake ref isn't a local path pin.

Requested by annika (infra.run) via dmatrix, hyperhive#2854.

frontend/packages/dashboard/src/home.js

@@ -48,6 +48,19 @@ async function init() {
     ident.textContent = parts.join(' / ');
     ident.hidden = false;
   }
+
+  // Rev line: absent when the flake ref isn't a local path pin (a bare
+  // `github:` url has no on-disk rev to canonicalize) — hidden rather
+  // than showing a placeholder in that case.
+  const rev = $('hive-rev');
+  if (rev && state.hyperhive_rev) {
+    const short = state.hyperhive_rev.length > 16
+      ? `…${state.hyperhive_rev.slice(-12)}`
+      : state.hyperhive_rev;
+    rev.textContent = `rev ${short}`;
+    rev.title = state.hyperhive_rev;
+    rev.hidden = false;
+  }
 }
 
 init();

frontend/packages/dashboard/src/index.html

@@ -30,6 +30,7 @@
   <header class="home-header">
     <p class="banner-thin" id="hive-identity" hidden></p>
     <pre class="banner">░▒▓█▓▒░  ░▒▓█▓▒░  H Y P E R H I V E  ·  H0M3  ░▒▓█▓▒░  ░▒▓█▓▒░</pre>
+    <p class="banner-thin" id="hive-rev" hidden></p>
   </header>
 
   <main class="home-main">