fix: raise header overlays above dashboard surfaces

backend/workflows/static/workflows/css/app_chrome.css

@@ -14,6 +14,9 @@
   box-sizing: border-box;
   width: min(var(--app-shell-width), 100%);
   margin: 0 auto 12px;
+  position: relative;
+  z-index: 30;
+  overflow: visible;
   display: flex;
   justify-content: space-between;
   align-items: flex-start;
@@ -137,6 +140,9 @@
   box-sizing: border-box;
   width: 100%;
   margin: 0;
+  position: relative;
+  z-index: 30;
+  overflow: visible;
   padding: 22px 24px 18px;
   border: 0;
   border-bottom: 1px solid rgba(217, 227, 238, 0.9);
@@ -174,6 +180,8 @@
   display: flex;
   margin-left: auto;
   flex: 0 0 auto;
+  position: relative;
+  z-index: 31;
   gap: 8px;
   flex-wrap: wrap;
   justify-content: flex-end;