fix: Remove top padding gap and add exit/logout to More page

Fixed 2 issues:

1. Top Padding Gap (pt-16 → removed)
   Problem: Mobile fullscreen had pt-16 padding creating gap at top
   Cause: Redundant padding when header is hidden in fullscreen
   Solution: Removed pt-16 from mobile fullscreen layout

   Before:
   <div className="flex flex-1 flex-col min-h-0 pt-16">

   After:
   <div className="flex flex-1 flex-col min-h-0">

   Result: No gap, submenu starts at top-0 ✓

2. Exit/Logout Buttons in More Page
   Problem: No way to exit fullscreen or logout from mobile
   Solution: Added context-aware button to More page

   WP-Admin Mode:
   - Shows "Exit Fullscreen" button
   - Exits fullscreen mode (back to normal WP-admin)

   Standalone Mode (PWA):
   - Shows "Logout" button
   - Redirects to WP-admin login

   Implementation:
   - Created AppContext to provide isStandalone and exitFullscreen
   - Wrapped Shell with AppProvider
   - More page uses useApp() to get context
   - Conditional rendering based on mode

Files Modified:
- App.tsx: Removed pt-16, added AppProvider
- AppContext.tsx: New context for app-level state
- More/index.tsx: Added Exit/Logout button

Result:
✅ No top gap in mobile fullscreen
✅ Exit fullscreen available in WP-admin mode
✅ Logout available in standalone mode
✅ Clean, functional mobile UX! 🎯

admin-spa/src/contexts/AppContext.tsx

@@ -0,0 +1,32 @@
+import React, { createContext, useContext, ReactNode } from 'react';
+
+interface AppContextType {
+  isStandalone: boolean;
+  exitFullscreen?: () => void;
+}
+
+const AppContext = createContext<AppContextType | undefined>(undefined);
+
+export function AppProvider({ 
+  children, 
+  isStandalone, 
+  exitFullscreen 
+}: { 
+  children: ReactNode; 
+  isStandalone: boolean; 
+  exitFullscreen?: () => void;
+}) {
+  return (
+    <AppContext.Provider value={{ isStandalone, exitFullscreen }}>
+      {children}
+    </AppContext.Provider>
+  );
+}
+
+export function useApp() {
+  const context = useContext(AppContext);
+  if (context === undefined) {
+    throw new Error('useApp must be used within an AppProvider');
+  }
+  return context;
+}