docs: Audit and cleanup documentation

## Task 1: Translation Support Audit ✅
- Audited all settings pages for translation support
- Found 3 pages missing `__` function: Store, Payments, Developer
- Most pages already have proper i18n implementation
- Action: Add translation support in next iteration

## Task 2: Documentation Cleanup ✅

### Created
- DOCS_AUDIT_REPORT.md - Comprehensive audit of 36 MD files
- TASKS_SUMMARY.md - Current tasks and progress tracking

### Deleted (12 obsolete docs)
Removed completed/superseded documentation:
- CUSTOMER_SETTINGS_404_FIX.md - Bug fixed
- MENU_FIX_SUMMARY.md - Menu implemented
- DASHBOARD_TWEAKS_TODO.md - Dashboard complete
- DASHBOARD_PLAN.md - Dashboard implemented
- SPA_ADMIN_MENU_PLAN.md - Menu implemented
- STANDALONE_ADMIN_SETUP.md - Standalone complete
- STANDALONE_MODE_SUMMARY.md - Duplicate doc
- SETTINGS_PAGES_PLAN.md - Superseded by V2
- SETTINGS_PAGES_PLAN_V2.md - Settings implemented
- SETTINGS_TREE_PLAN.md - Navigation implemented
- SETTINGS_PLACEMENT_STRATEGY.md - Strategy finalized
- TAX_NOTIFICATIONS_PLAN.md - Merged into notification strategy

### Result
- **Before:** 36 documents
- **After:** 24 documents
- **Reduction:** 33% fewer docs
- **Benefit:** Clearer focus, easier navigation

### Remaining Docs
- 15 essential docs (core architecture, guides)
- 9 docs to consolidate later (low priority)

## Task 3: Notification System - Ready
- Read NOTIFICATION_STRATEGY.md
- Created implementation plan in TASKS_SUMMARY.md
- Ready to start Phase 1 implementation

---

**Next:** Implement notification core framework

admin-spa/src/App.tsx

@@ -522,6 +522,9 @@ function Shell() {
   // Check if current route is More page (no submenu needed)
   const isMorePage = location.pathname === '/more';
 
+  const submenuTopClass = fullscreen ? 'top-0' : 'top-[calc(7rem+32px)]';
+  const submenuZIndex = fullscreen ? 'z-50' : 'z-40';
+
   return (
     <AppProvider isStandalone={isStandalone} exitFullscreen={exitFullscreen}>
       {!isStandalone && <ShortcutsBinder onToggle={toggle} />}
@@ -550,7 +553,7 @@ function Shell() {
           ) : (
             <div className="flex flex-1 flex-col min-h-0">
               {/* Flex wrapper: mobile = col (PageHeader first), desktop = col-reverse (SubmenuBar first) */}
-              <div className="flex flex-col md:flex-col-reverse">
+              <div className={`flex flex-col md:flex-col-reverse sticky ${submenuTopClass} ${submenuZIndex}`}>
                 <PageHeader fullscreen={true} />
                 {!isMorePage && (isDashboardRoute ? (
                   <DashboardSubmenuBar items={main.children} fullscreen={true} />
@@ -571,7 +574,7 @@ function Shell() {
           <div className="flex flex-1 flex-col min-h-0">
             <TopNav />
             {/* Flex wrapper: mobile = col (PageHeader first), desktop = col-reverse (SubmenuBar first) */}
-            <div className="flex flex-col md:flex-col-reverse">
+            <div className={`flex flex-col md:flex-col-reverse sticky ${submenuTopClass} ${submenuZIndex}`}>
               <PageHeader fullscreen={false} />
               {isDashboardRoute ? (
                 <DashboardSubmenuBar items={main.children} fullscreen={false} />