feat(ui): replace AppLayout with ContextStrip + rebuilt Sidebar

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

frontend/src/components/layout/AppLayout.tsx

@@ -1,6 +1,6 @@
 import { type ReactNode } from 'react'
 import { Sidebar } from './Sidebar'
-import { Header } from './Header'
+import { ContextStrip } from './ContextStrip'
 import { ShortcutsDialog } from './ShortcutsDialog'
 import { CommandPalette } from '@/components/command-palette/CommandPalette'
 import { Toaster } from '@/components/ui/toast'
@@ -20,8 +20,10 @@ export function AppLayout({ children }: AppLayoutProps) {
       </a>
       <Sidebar />
       <div className="flex flex-col flex-1 min-w-0 overflow-hidden">
-        <Header />
-        <main id="main-content" tabIndex={-1} className="flex-1 overflow-auto p-2 sm:p-4">{children}</main>
+        <ContextStrip />
+        <main id="main-content" tabIndex={-1} className="flex-1 overflow-auto p-5">
+          {children}
+        </main>
       </div>
       <Toaster />
       <CommandPalette />

frontend/src/components/layout/Header.tsx

@@ -1,3 +1,4 @@
+// DEPRECATED: Replaced by ContextStrip.tsx — keeping for reference during transition
 import { useEffect } from 'react'
 import { useNavigate, Link } from '@tanstack/react-router'
 import { LogOut, ChevronDown, User, Search, Sun, Moon, RefreshCw, Menu, Settings } from 'lucide-react'