fix: collapse Brain sidebar sub-menu when navigating away from Brain page

Switch Brain Collapsible from uncontrolled defaultOpen to controlled open
prop derived from activeView, so the sub-menu only expands on Brain pages.

Author: marian2js

apps/desktop/src/app/shell/AppSidebar.tsx

@@ -238,7 +238,7 @@ export function AppSidebar({
 
               {/* Brain — collapsible */}
               <Collapsible
-                defaultOpen={activeView === "brain"}
+                open={activeView === "brain"}
                 asChild
                 className="group/collapsible"
               >

test/ui/sidebar-brain-subnav.test.ts

@@ -68,4 +68,16 @@ describe("Sidebar Brain sub-navigation", () => {
     // The sidebar should use sidebar- prefixed tokens which adapt to theme
     expect(sidebarSrc).toMatch(/sidebar-accent|sidebar-foreground|sidebar-primary/);
   });
+
+  // AC6: Brain sub-menu collapses when navigating away from Brain page
+  it("uses controlled open prop derived from activeView, not defaultOpen", () => {
+    // The Collapsible wrapping the Brain section must use the controlled `open`
+    // prop so that expand/collapse state tracks the current route, collapsing
+    // when the user navigates away from Brain pages.
+    // It should NOT use defaultOpen (which only sets initial state and then
+    // Radix manages it internally, causing the menu to stay open on all pages).
+    expect(sidebarSrc).toMatch(/open=\{activeView\s*===\s*["']brain["']\}/);
+    // Ensure defaultOpen is NOT used for the Brain collapsible
+    expect(sidebarSrc).not.toMatch(/defaultOpen=\{activeView\s*===\s*["']brain["']\}/);
+  });
 });