What this PR does

Before this PR:

• The v2 sidebar was a simple inline implementation with basic menu items using Tailwind classes directly in the app-level Sidebar.tsx
• No reusable sidebar component existed in @cherrystudio/ui
• Missing route definitions for /app/agents and /app/openclaw caused "Page Not Found" when clicking those menu items

After this PR:

• Adds a full-featured Sidebar component to packages/ui/src/components/sidebar/ with:
  • Responsive layouts: icon-only, vertical-card, and full-width modes based on sidebar width
  • Drag support: useSidebarDrag hook for docking/undocking tabs to/from the sidebar
  • Tab management: useSidebarTabs hook for managing sidebar tabs and mini-app tabs
  • Resizable: Users can drag to resize the sidebar between different layout modes
• Refactors app-level Sidebar.tsx to consume the new UISidebar component
• Adds CSS custom properties for sidebar theming (light/dark mode)
• Includes the upstream sidebar-simplify fixes (route definitions for agents/openclaw)

Why we need it and why it was done in this way

The v2 UI migration requires moving from antd/styled-components to @cherrystudio/ui (Tailwind + Shadcn). The sidebar is a core navigation component that benefits from being a reusable, well-structured UI primitive in the shared package.

The following tradeoffs were made:

• Built as a standalone component in packages/ui rather than inline in the app, to enable reuse across windows (main, mini) and easier testing

The following alternatives were considered:

• Keeping the inline Tailwind implementation from sidebar-simplify — rejected because it doesn't support responsive layout modes or drag interactions

Breaking changes

None. This builds on top of the sidebar-simplify refactor.

Special notes for your reviewer

• This is a draft PR — the sidebar component is a first version and may need further iteration
• Built on top of refactor/v2/sidebar-simplify (upstream) which fixed the agents/openclaw routing
• The useSidebarDrag and useSidebarTabs hooks are not yet fully wired into the app-level code

Checklist

• PR: The PR description is expressive enough and will help future contributors
• Code: Write code that humans can understand and Keep it simple
• Refactor: You have left the code cleaner than you found it (Boy Scout Rule)
• Upgrade: Impact of this change on upgrade flows was considered and addressed if required
• Documentation: A user-guide update was considered and is present or not required
• Self-review: I have reviewed my own code before requesting review from others

Release note

```release-note
NONE
```