fix(e5): stop the filter dropdown flashing at the origin before it positions

The combi-input popover flashed in the top-left corner for a frame, then
jumped into place. Two causes, both confirmed with a per-frame capture in
the browser:

1. The panel painted before floating-ui computed a position — gated its
   visibility on `isPositioned` (hidden until positioned), same as
   PopoverSurface.
2. The bigger one: the `popIn` entrance animation animates `transform`
   (scale/translateY), and it sat on the SAME element floating-ui positions
   via `transform` — so during the 0.16s animation the keyframes OVERRODE
   the translate(x,y) and the panel rendered at the origin. Moved the glass
   styling + popIn onto an inner child, leaving the positioned element's
   transform untouched.

Frame capture after the fix: frame 0 hidden, first visible frame already at
translate(82,474) — never visible at the origin. Also gave the size
middleware a min width for a narrow rail.

frontend/src/components/MultiSelectChips.tsx

@@ -51,7 +51,7 @@ export default function MultiSelectChips({
   const inputRef = useRef<HTMLInputElement>(null);
   const fade = useScrollFade();
 
-  const { refs, floatingStyles, context } = useFloating({
+  const { refs, floatingStyles, context, isPositioned } = useFloating({
     open,
     onOpenChange: setOpen,
     placement: "bottom-start",
@@ -62,12 +62,10 @@ export default function MultiSelectChips({
       shift({ padding: 8 }),
       size({
         padding: 8,
-        apply({ rects, elements, availableHeight }) {
-          // Match the field width and cap to the space below (or 320px, whichever is smaller).
-          Object.assign(elements.floating.style, {
-            width: `${rects.reference.width}px`,
-            maxHeight: `${Math.min(availableHeight, 320)}px`,
-          });
+        apply({ rects, elements }) {
+          // Match the field width (with a sane minimum for a very narrow rail); the inner scroll box
+          // owns the height cap (max-h-64).
+          elements.floating.style.width = `${Math.max(rects.reference.width, 192)}px`;
         },
       }),
     ],
@@ -166,15 +164,22 @@ export default function MultiSelectChips({
         <FloatingPortal>
           <div
             ref={refs.setFloating}
-            style={floatingStyles}
+            // Keep the panel hidden until floating-ui has computed a real position — otherwise the first
+            // frame paints it at the container's top-left before autoUpdate runs. (isPositioned guard,
+            // same as PopoverSurface.)
+            style={{ ...floatingStyles, visibility: isPositioned ? "visible" : "hidden" }}
             {...getFloatingProps()}
             aria-label={label}
-            className="glass-menu z-popover min-w-48 rounded-xl p-1.5 shadow-lg animate-[popIn_0.16s_ease]"
+            className="z-popover"
           >
+            {/* The entrance animation + glass styling live ONE level in: popIn animates `transform`
+                (scale/translateY), which on the positioned element itself would OVERRIDE floating-ui's
+                transform-based position and flash the panel at the origin for the animation's duration.
+                Keeping it on a child leaves the outer element's position transform untouched. */}
             <div
               ref={fade.ref}
               style={fade.style}
-              className="max-h-64 overflow-y-auto no-scrollbar"
+              className="glass-menu max-h-64 w-full overflow-y-auto rounded-xl p-1.5 no-scrollbar shadow-lg animate-[popIn_0.16s_ease]"
             >
               {filtered.length === 0 ? (
                 <p className="px-2 py-1.5 text-xs text-muted">