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Removed completed/superseded documentation: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- SETTINGS_PAGES_PLAN.md - Superseded by V2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/components/nav/SubmenuBar.tsx

@@ -17,7 +17,7 @@ export default function SubmenuBar({ items = [], fullscreen = false, headerVisib
   const topClass = fullscreen ? 'top-0' : 'top-[calc(7rem+32px)]';
 
   return (
-    <div data-submenubar className={`border-b border-border bg-background md:bg-background/95 md:backdrop-blur md:supports-[backdrop-filter]:bg-background/60 sticky ${topClass} z-20`}>
+    <div data-submenubar className={`border-b border-border bg-background md:bg-background/95 md:backdrop-blur md:supports-[backdrop-filter]:bg-background/60`}>
       <div className="px-4 py-2">
         <div className="flex gap-2 overflow-x-auto no-scrollbar">
           {items.map((it) => {