feat: redesign Sidebar with hierarchical trees, starring, and collapsible sections

Replace flat app/route/agent lists with expandable tree navigation.
Apps contain their routes and agents hierarchically. Add localStorage-
backed starring with composite keys for uniqueness. Persist expand
state to sessionStorage across page navigations. Add collapsible
section headers, remove button on starred items, and parent app
context labels. Create stub pages for /apps/:id, /agents/:id,
/admin, /api-docs. Consolidate duplicated sidebar data into
shared mock. Widen sidebar from 220px to 260px.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

COMPONENT_GUIDE.md

@@ -34,10 +34,10 @@
 - Removable label → **Tag**
 
 ### "I need navigation"
-- App-level sidebar nav → **Sidebar** (via AppShell)
+- App-level sidebar nav → **Sidebar** (via AppShell) — hierarchical trees with starring
 - Breadcrumb trail → **Breadcrumb**
 - Paginated data → **Pagination** (standalone) or **DataTable** (built-in pagination)
-- Hierarchical tree navigation → **TreeView**
+- Hierarchical tree navigation → **TreeView** (generic) or **SidebarTree** (sidebar-specific, internal)
 
 ### "I need floating content"
 - Tooltip on hover → **Tooltip**
@@ -186,7 +186,7 @@ TreeView for hierarchical data (Application → Routes → Processors)
 | Component | Purpose |
 |-----------|---------|
 | AppShell | Page shell: sidebar + topbar + main + optional detail panel |
-| Sidebar | App navigation with apps, routes, agents sections |
+| Sidebar | Hierarchical navigation with Applications/Agents trees, starring, search filter, bottom links. Props: `apps: SidebarApp[]` (hierarchical — apps contain routes and agents) |
 | TopBar | Header bar with breadcrumb, environment, user info |
 
 ## Import Paths