Dropdown menus paint under later glass panels - portal them out

The Signals > Setups filter dropdowns (Direction, Recommended Action)
opened UNDER the panels below: glass containers use backdrop-filter,
which creates a stacking context, so the menu's z-50 could never
compete with later sibling panels regardless of value.

The menu now portals to document.body with fixed positioning tracked
against the trigger (re-measured on scroll/resize), and click-outside
accounts for the portaled node. Applies to every Dropdown usage.
Menu background also updated from the old green-tinted #151911 to the
Horizon #14161f.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/components/ui/Dropdown.tsx

@@ -1,4 +1,5 @@
 import { useEffect, useRef, useState } from 'react';
+import { createPortal } from 'react-dom';
 
 export interface DropdownOption {
   value: string;
@@ -17,8 +18,12 @@ interface DropdownProps {
 
 /**
  * Fully dark, custom dropdown — replaces native <select>, whose popup list
- * can't be reliably styled (white background on Windows). Button + absolutely
- * positioned menu, click-outside and Escape to close.
+ * can't be reliably styled (white background on Windows).
+ *
+ * The menu is PORTALED to document.body with fixed positioning: glass panels
+ * use backdrop-filter, which creates a stacking context, so an absolutely
+ * positioned menu inside one would paint UNDER any later sibling panel no
+ * matter its z-index.
  */
 export function Dropdown({
   value,
@@ -30,14 +35,34 @@ export function Dropdown({
   placeholder = 'Select…',
 }: DropdownProps) {
   const [open, setOpen] = useState(false);
+  const [rect, setRect] = useState<{ top: number; left: number; width: number } | null>(null);
   const rootRef = useRef<HTMLDivElement>(null);
+  const menuRef = useRef<HTMLUListElement>(null);
 
   const selected = options.find((o) => o.value === value);
 
+  // Track the button's viewport position while open (scroll/resize).
+  useEffect(() => {
+    if (!open) return;
+    const measure = () => {
+      const r = rootRef.current?.getBoundingClientRect();
+      if (r) setRect({ top: r.bottom + 4, left: r.left, width: r.width });
+    };
+    measure();
+    window.addEventListener('scroll', measure, true);
+    window.addEventListener('resize', measure);
+    return () => {
+      window.removeEventListener('scroll', measure, true);
+      window.removeEventListener('resize', measure);
+    };
+  }, [open]);
+
   useEffect(() => {
     if (!open) return;
     const onDocClick = (e: MouseEvent) => {
-      if (rootRef.current && !rootRef.current.contains(e.target as Node)) setOpen(false);
+      const t = e.target as Node;
+      if (rootRef.current?.contains(t) || menuRef.current?.contains(t)) return;
+      setOpen(false);
     };
     const onKey = (e: KeyboardEvent) => {
       if (e.key === 'Escape') setOpen(false);
@@ -74,10 +99,12 @@ export function Dropdown({
         </svg>
       </button>
 
-      {open && (
+      {open && rect && createPortal(
         <ul
+          ref={menuRef}
           role="listbox"
-          className="absolute z-50 mt-1 max-h-64 w-full overflow-auto rounded-lg border border-white/[0.1] bg-[#151911] p-1 shadow-2xl shadow-black/50"
+          style={{ position: 'fixed', top: rect.top, left: rect.left, width: rect.width }}
+          className="z-50 max-h-64 overflow-auto rounded-lg border border-white/[0.1] bg-[#14161f] p-1 shadow-2xl shadow-black/50"
         >
           {options.map((opt) => {
             const isSelected = opt.value === value;
@@ -109,7 +136,8 @@ export function Dropdown({
               </li>
             );
           })}
-        </ul>
+        </ul>,
+        document.body,
       )}
     </div>
   );