fix: hide update banner + app-header during cooking mode; raise overlay z-index

- .cooking-overlay z-index 500 → 99998 (above everything)
- body.cooking-mode-active: hide #_evershelf_update_banner and .app-header
- .cooking-mode-active #modal-overlay z-index 600 → 99999

assets/css/style.css

@@ -2505,7 +2505,7 @@ body {
 
 /* Raise modal above cooking overlay when in cooking mode */
 .cooking-mode-active #modal-overlay {
-    z-index: 600;
+    z-index: 99999;
 }
 
 .modal-content {
@@ -3605,7 +3605,7 @@ body {
     position: fixed;
     inset: 0;
     background: #0a0a0a;
-    z-index: 500;
+    z-index: 99998; /* above every fixed UI: header, update banner, etc. */
     display: flex;
     flex-direction: column;
     color: #fff;
@@ -3613,6 +3613,12 @@ body {
     touch-action: pan-y;
 }
 
+/* Hide update banner, app-header and any other fixed-top chrome while in cooking mode */
+body.cooking-mode-active #_evershelf_update_banner,
+body.cooking-mode-active .app-header {
+    display: none !important;
+}
+
 .cooking-header {
     display: flex;
     align-items: center;