fix(ui): repaint transport-bar uptime as soon as /health responds

The inline transport-uptime ticker only repainted on its 1 s setInterval,
so the field could sit on - for up to ~1 s after page load (and much
longer if init's first /health response landed between ticks - the next
seed then had to wait for the 10 s connection-monitor poll). Dispatch a
serverUptimeChanged DOM event when window.__serverUptime is seeded and
let the inline IIFE re-render on receipt, so the value appears as soon
as the response arrives.

server/src/ledgrab/static/js/core/api.ts

@@ -344,6 +344,13 @@ export async function loadServerInfo() {
                 uptimeSec: data.uptime_seconds,
                 recordedAtPerf: performance.now(),
             };
+            // Wake the inline transport-uptime ticker immediately instead of
+            // waiting up to a full second for its setInterval tick. Without
+            // this nudge the field can stay on "—" for ~1 s after page load
+            // (and up to 10 s if init's first /health response arrives just
+            // after a tick and the user has to wait for the next connection-
+            // monitor poll to seed it).
+            document.dispatchEvent(new CustomEvent('serverUptimeChanged'));
         }
 
         // Demo mode detection

server/src/ledgrab/templates/index.html

@@ -570,6 +570,9 @@
             }
             render();
             setInterval(render, 1000);
+            // Repaint as soon as api.ts seeds window.__serverUptime, so the
+            // field doesn't have to wait up to a second for the next tick.
+            document.addEventListener('serverUptimeChanged', render);
         })();
 
         // Transport-bar poll-interval control — cycles through 1/2/5/10s