fix(a11y): every side-panel pin names its panel; the tab under an open card leaves the tree

The card's own pin and the drawer's still said 'Unpin panel' / 'Pin panel open' after the edge tab
learned the title (F6). Naming them too made two buttons share a name, because the invisible tab
under an open card was still in the accessibility tree: it is now aria-hidden as well as out of
the Tab order. The generic sidebar.pin / unpin keys are gone.

frontend/src/components/ui/SidePanel.tsx

@@ -160,7 +160,10 @@ export default function SidePanel({
                   );
               }
         }
+        // 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}
+        aria-hidden={expanded || undefined}
         aria-label={
           drawerMode
             ? t("sidebar.openPanel", { title })
@@ -197,7 +200,7 @@ export default function SidePanel({
               Module actions live on their own row below so the title always has room. */}
           <div className="flex items-center gap-1.5 px-3 py-2.5 border-b border-border/60 flex-none">
             <IconButton
-              label={pinned ? t("sidebar.unpin") : t("sidebar.pin")}
+              label={pinned ? t("sidebar.unpinNamed", { title }) : t("sidebar.pinNamed", { title })}
               size="sm"
               variant="ghost"
               onClick={onToggleCollapse}
@@ -245,7 +248,7 @@ export default function SidePanel({
             <>
               {pinRoom && (
                 <IconButton
-                  label={t("sidebar.pin")}
+                  label={t("sidebar.pinNamed", { title })}
                   size="sm"
                   variant="ghost"
                   onClick={() => {