fix(ui): let revealed panels own their side and keep Cockpit's left strip

A panel a feature opens (Street Level's viewer, a selected radio station)
now becomes its side's open panel instead of being collapsed again by the
next layout pass. Cockpit keeps showing its collapsed Data Layers strip,
which Cyber's Cockpit layout aligns to, and Cyber's focus layout no longer
re-shows collapsed left panels. Both sidebars share one accordion helper.

src/ui/rightPanelRail.js

@@ -5,6 +5,7 @@ import {
 import { resolveHudRailLayout } from './panelRailGeometry.js';
 
 import { displayPanelScroller } from './displayPanelScroll.js';
+import { settleSideAccordion } from './panelAccordion.js';
 
 const pendingCollapseRetries = new WeakSet();
 
@@ -86,31 +87,16 @@ export function layoutRightPanelRail({
       onCollapse(panel);
     }
   }
-  // One panel is open per desktop side. Normalize restored state without
-  // overwriting saved panel preferences; this marker is distinct from
-  // Tactical's space-based collapse. Phones present the rail as tab sheets
-  // that show several panels at once.
+  // One panel is open per desktop side; this marker is distinct from
+  // Tactical's space-based collapse.
   const isMobile = windowRef.matchMedia('(max-width: 720px)').matches;
-  if (!isMobile) {
-    const expanded = panels.filter(
-      (panel) => !panel.classList.contains('collapsed'),
-    );
-    const owner =
-      expanded.find((panel) => panel.id === preferredPanelId) ||
-      expanded.find((panel) => panel.contains(documentRef?.activeElement)) ||
-      expanded[0];
-    for (const panel of expanded) {
-      if (panel === owner) continue;
-      panel.classList.add('collapsed', 'accordion-collapsed');
-      onCollapse(panel);
-    }
-  } else {
-    for (const panel of panels) {
-      if (!panel.classList.contains('accordion-collapsed')) continue;
-      panel.classList.remove('collapsed', 'accordion-collapsed');
-      onCollapse(panel);
-    }
-  }
+  settleSideAccordion({
+    panels,
+    enabled: !isMobile,
+    preferredPanelId,
+    documentRef,
+    onCollapse,
+  });
   // The desktop panel rail lists every panel, so collapsed ones are hidden.
   // Phones present the rail as tab sheets (mobileShell.js), which choose what
   // shows; hiding collapsed siblings would empty a sheet and its a11y tree.