refactor(ui): consolidate unified-sidebar into sidebar folder

Merge the unified-sidebar implementation into the standard sidebar
folder structure. The unified sidebar becomes the canonical sidebar
with improved features including collapsible sections, scroll
indicators, and enhanced mobile support.

- Delete old sidebar.tsx
- Move unified-sidebar components to sidebar/components
- Rename UnifiedSidebar to Sidebar
- Update all imports in __root.tsx
- Remove redundant unified-sidebar folder

apps/ui/src/components/layout/sidebar/hooks/use-navigation.ts

@@ -13,6 +13,7 @@ import {
   Network,
   Bell,
   Settings,
+  Home,
 } from 'lucide-react';
 import type { NavSection, NavItem } from '../types';
 import type { KeyboardShortcut } from '@/hooks/use-keyboard-shortcuts';
@@ -174,13 +175,30 @@ export function useNavigation({
     }
 
     const sections: NavSection[] = [
+      // Dashboard - standalone at top
+      {
+        label: '',
+        items: [
+          {
+            id: 'dashboard',
+            label: 'Dashboard',
+            icon: Home,
+          },
+        ],
+      },
+      // Project section - expanded by default
       {
         label: 'Project',
         items: projectItems,
+        collapsible: true,
+        defaultCollapsed: false,
       },
+      // Tools section - collapsed by default
       {
         label: 'Tools',
         items: visibleToolsItems,
+        collapsible: true,
+        defaultCollapsed: true,
       },
     ];
 
@@ -203,6 +221,8 @@ export function useNavigation({
             shortcut: shortcuts.githubPrs,
           },
         ],
+        collapsible: true,
+        defaultCollapsed: true,
       });
     }