ui: remove top header, move CPU/RAM/disk + clock into the footer

Header bar dropped from all pages; brand, system stats (#sys-stats) and clock
(#clock) now live in the 22px footer next to the version. .layout fills the
full height minus the footer. ensureFooter runs before startClock/refreshStats
so the moved elements exist when populated.

VERSION 0.0.136.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/static/app.js

@@ -146,6 +146,8 @@ function ensureFooter() {
   f.className = "app-footer";
   f.innerHTML = `<span class="brand">CoRE<span>.Vision</span></span>` +
                 `<span class="spacer"></span>` +
+                `<span class="stats" id="sys-stats"></span>` +
+                `<span class="clock" id="clock"></span>` +
                 `<span id="footer-version"></span>`;
   document.body.appendChild(f);
 }
@@ -2046,10 +2048,10 @@ function initTabs() {
 
 // ── загрузка страницы ───────────────────────────────────────────
 document.addEventListener("DOMContentLoaded", async () => {
+  ensureVersionEl();
+  ensureFooter();                 // создаёт футер с #sys-stats/#clock до их заполнения
   startClock();
   bindLogout();
-  ensureVersionEl();
-  ensureFooter();
   refreshStats(); setInterval(refreshStats, 5000);
   applyGridMenuLimit();
   const page = document.body.dataset.page;