fix(playlists): flip the add-to-playlist popover up when it would overflow

The popover was always positioned below its trigger, so on cards near the bottom
of the viewport it ran off-screen. Measure the panel's real height and open it
upward (clamped to the viewport) when there isn't room below; also clamp the
horizontal position.

frontend/src/components/AddToPlaylist.tsx

@@ -1,4 +1,4 @@
-import { useEffect, useRef, useState } from "react";
+import { useEffect, useLayoutEffect, useRef, useState } from "react";
 import { createPortal } from "react-dom";
 import { useTranslation } from "react-i18next";
 import { useQuery, useQueryClient } from "@tanstack/react-query";
@@ -29,14 +29,27 @@ export default function AddToPlaylist({
     enabled: open,
   });
 
+  // Re-place once the panel is actually rendered (so we know its real height) and whenever
+  // its content — hence height — changes, so the flip-above decision uses the true size.
+  useLayoutEffect(() => {
+    if (open) place();
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [open, membership.data]);
+
   function place() {
     const r = triggerRef.current?.getBoundingClientRect();
     if (!r) return;
     const width = 240;
-    setCoords({
+    const margin = 8;
-      top: Math.round(r.bottom + 6),
+    // Use the panel's real height once it's mounted; estimate on the first open.
-      left: Math.round(Math.min(r.left, window.innerWidth - width - 8)),
+    const h = panelRef.current?.offsetHeight ?? 300;
-    });
+    let top = r.bottom + 6;
+    if (top + h > window.innerHeight - margin) {
+      // Not enough room below — open upward, clamped to the viewport.
+      top = Math.max(margin, r.top - h - 6);
+    }
+    const left = Math.min(Math.max(margin, r.left), window.innerWidth - width - margin);
+    setCoords({ top: Math.round(top), left: Math.round(left) });
   }
 
   function toggleOpen(e: React.MouseEvent) {