refactor(ui): move user info to top-right app header

- Create UserHeader component to display user info and logout button
- Move 'Logged in as: user' from sidebar to app-header in top-right
- Remove user info display from BookmarkList and Bookmarks components
- Simplify bookmarks-header layout (only contains collapse button now)
- Update CSS to display user info and logout button inline with proper spacing

src/components/UserHeader.tsx

@@ -0,0 +1,47 @@
+import React from 'react'
+import { Hooks } from 'applesauce-react'
+import { useEventModel } from 'applesauce-react/hooks'
+import { Models } from 'applesauce-core'
+import { faRightFromBracket } from '@fortawesome/free-solid-svg-icons'
+import IconButton from './IconButton'
+
+interface UserHeaderProps {
+  onLogout: () => void
+}
+
+const UserHeader: React.FC<UserHeaderProps> = ({ onLogout }) => {
+  const activeAccount = Hooks.useActiveAccount()
+  const profile = useEventModel(Models.ProfileModel, activeAccount ? [activeAccount.pubkey] : null)
+
+  const formatUserDisplay = () => {
+    if (!activeAccount) return 'Unknown User'
+
+    if (profile?.name) {
+      return profile.name
+    }
+    if (profile?.display_name) {
+      return profile.display_name
+    }
+    if (profile?.nip05) {
+      return profile.nip05
+    }
+
+    return `${activeAccount.pubkey.slice(0, 8)}...${activeAccount.pubkey.slice(-8)}`
+  }
+
+  return (
+    <div className="app-header">
+      <p className="user-info">Logged in as: {formatUserDisplay()}</p>
+      <IconButton
+        icon={faRightFromBracket}
+        onClick={onLogout}
+        title="Logout"
+        ariaLabel="Logout"
+        variant="ghost"
+      />
+    </div>
+  )
+}
+
+export default UserHeader
+