feat(#112): hide sidebar, topbar, cmd palette on admin pages

Pass null as sidebar prop, guard TopBar and CommandPalette with
!isAdminPage, and remove conditional admin padding from main element.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ui/src/components/LayoutShell.tsx

@@ -296,29 +296,33 @@ function LayoutContent() {
   return (
     <AppShell
       sidebar={
-        <Sidebar apps={sidebarApps} onNavigate={handleSidebarNavigate} />
+        isAdminPage ? null : <Sidebar apps={sidebarApps} onNavigate={handleSidebarNavigate} />
       }
     >
-      <TopBar
-        breadcrumb={breadcrumb}
-        user={username ? { name: username } : undefined}
-        onLogout={handleLogout}
-      />
-      <CommandPalette
-        open={paletteOpen}
-        onClose={() => setPaletteOpen(false)}
-        onOpen={() => setPaletteOpen(true)}
-        onSelect={handlePaletteSelect}
-        onSubmit={handlePaletteSubmit}
-        onQueryChange={setPaletteQuery}
-        data={searchData}
-      />
+      {!isAdminPage && (
+        <TopBar
+          breadcrumb={breadcrumb}
+          user={username ? { name: username } : undefined}
+          onLogout={handleLogout}
+        />
+      )}
+      {!isAdminPage && (
+        <CommandPalette
+          open={paletteOpen}
+          onClose={() => setPaletteOpen(false)}
+          onOpen={() => setPaletteOpen(true)}
+          onSelect={handlePaletteSelect}
+          onSubmit={handlePaletteSubmit}
+          onQueryChange={setPaletteQuery}
+          data={searchData}
+        />
+      )}
 
       {!isAdminPage && (
         <ContentTabs active={scope.tab} onChange={setTab} scope={scope} />
       )}
 
-      <main style={{ flex: 1, display: 'flex', flexDirection: 'column', overflow: 'hidden', minHeight: 0, padding: isAdminPage ? '1.5rem' : 0 }}>
+      <main style={{ flex: 1, display: 'flex', flexDirection: 'column', overflow: 'hidden', minHeight: 0, padding: 0 }}>
         <Outlet />
       </main>
     </AppShell>