fix(side-panel): the key's focus steps into the peeked card in the commit that opens it

A frame later never came in a page the browser was not painting (measured: a hidden page runs no
requestAnimationFrame), and the focus stayed on the inert tab under the card.

frontend/src/components/ui/SidePanel.tsx

@@ -1,4 +1,4 @@
-import { useRef, useState, type ReactNode } from "react";
+import { useLayoutEffect, useRef, useState, type ReactNode } from "react";
 import { useTranslation } from "react-i18next";
 import { Check, Pencil, Pin, PinOff, RotateCcw } from "lucide-react";
 import { useScrollFade } from "../../lib/useScrollFade";
@@ -65,6 +65,7 @@ export default function SidePanel({
 }) {
   const { t } = useTranslation();
   const cardRef = useRef<HTMLElement>(null);
+  const tabRef = useRef<HTMLButtonElement>(null);
   const fade = useScrollFade();
   const peek = useHoverFocusWithin();
   const drawerMode = useMediaQuery(DRAWER_QUERY, false);
@@ -77,6 +78,16 @@ export default function SidePanel({
   // Turning the tablet to a width where the panel is a card again, or pinning it, ends the drawer —
   // adjusted during render, so it cannot come back open on the next turn.
   if (drawerOpen && (!drawerMode || pinned)) setDrawerOpen(false);
+  // A key landing on the tab peeks the card open over it, and the tab then goes inert below — with
+  // the focus still on it: a hidden control, out of the tree, that Enter still pinned (round 2, F1).
+  // The focus steps into the card as it opens, onto its pin: the same control. In the commit that
+  // mounts the card, not a frame later — a frame never comes in a page the browser is not painting.
+  useLayoutEffect(() => {
+    const tab = tabRef.current;
+    if (!expanded || pinned || drawerMode || !tab || document.activeElement !== tab) return;
+    if (tab.matches(":focus-visible"))
+      cardRef.current?.querySelector<HTMLElement>("button")?.focus();
+  }, [expanded, pinned, drawerMode]);
 
   const titleNode = onTitleClick ? (
     <Pressable
@@ -160,15 +171,7 @@ export default function SidePanel({
                   );
               }
         }
-        // A key landing on the tab peeks the card open over it, and the tab then goes inert below —
-        // with the focus still on it: a hidden control, out of the tree, that Enter still pinned
-        // (round 2, F1). The focus steps into the card instead, onto its pin: the same control.
-        onFocus={(e) => {
-          if (drawerMode || pinned || !e.currentTarget.matches(":focus-visible")) return;
-          requestAnimationFrame(() =>
-            cardRef.current?.querySelector<HTMLElement>("button")?.focus(),
-          );
-        }}
+        ref={tabRef}
         // Under an open card the tab is transparent and inert: out of the Tab order AND of the
         // accessibility tree, where it would repeat the card's own pin button by name.
         tabIndex={expanded ? -1 : undefined}