Refactor: Improve header loading and image rendering

Add early JS to populate header elements and optimize image loading.

Co-authored-by: mathieumoran1 <[email protected]>

public/js/app_header_boot.js

@@ -0,0 +1,54 @@
+// Runs early (defer) to populate the navbar before page-specific JS.
+// Goal: avoid "late" header updates that look like flicker.
+(function () {
+  function base64UrlToJson(b64url) {
+    const s = String(b64url || '')
+      .replace(/-/g, '+')
+      .replace(/_/g, '/');
+    const padded = s + '='.repeat((4 - (s.length % 4)) % 4);
+    return JSON.parse(atob(padded));
+  }
+
+  function decodeJwtPayload(token) {
+    const parts = String(token || '').split('.');
+    if (parts.length < 2) return null;
+    try { return base64UrlToJson(parts[1]); } catch (_) { return null; }
+  }
+
+  function isExpired(decoded) {
+    const exp = Number(decoded?.exp);
+    if (!Number.isFinite(exp) || exp <= 0) return false;
+    const now = Math.floor(Date.now() / 1000);
+    return exp < now;
+  }
+
+  const token = localStorage.getItem('auth_token');
+  if (!token) return;
+
+  const decoded = decodeJwtPayload(token);
+  if (!decoded) return;
+
+  // Fast-path redirect checks (match page scripts behavior).
+  if (decoded.mustChangePassword && !/\/change-password\.html(\?|#|$)/.test(window.location.pathname)) {
+    window.location.href = '/change-password.html';
+    return;
+  }
+  if (isExpired(decoded)) {
+    try { localStorage.removeItem('auth_token'); } catch (_) {}
+    if (!/\/index\.html$/.test(window.location.pathname) && window.location.pathname !== '/') {
+      window.location.href = '/';
+    }
+    return;
+  }
+
+  const nameEl = document.getElementById('user-name');
+  if (nameEl && !nameEl.textContent) {
+    nameEl.textContent = decoded.name || '';
+  }
+
+  const adminLink = document.getElementById('admin-control-link');
+  if (adminLink && decoded.admin) {
+    adminLink.classList.remove('d-none');
+  }
+})();
+