fix: CRITICAL - Memoize all context values to stop infinite loops

THE BIGGER PICTURE - Root Cause Analysis:

Problem Chain:
1. FABContext value recreated every render
2. All FAB consumers re-render
3. Dashboard re-renders
4. useFABConfig runs
5. Creates new icon/callbacks
6. Triggers FABContext update
7. INFINITE LOOP!

The Bug (in BOTH contexts):
<Context.Provider value={{ config, setFAB, clearFAB }}>
                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                         NEW object every render!

Every time Provider re-renders:
- Creates NEW value object
- All consumers see "new" value
- All consumers re-render
- Causes more Provider re-renders
- INFINITE LOOP!

The Fix:
const setFAB = useCallback(..., []); // Stable function
const clearFAB = useCallback(..., []); // Stable function
const value = useMemo(() => ({ config, setFAB, clearFAB }), [config, setFAB, clearFAB]);
              ^^^^^^^
              Only creates new object when dependencies actually change!

<Context.Provider value={value}>
                        ^^^^^^^
                        Stable reference!

Why This is Critical:
Context is at the TOP of the component tree:
App
  └─ FABProvider ← Bug here affects EVERYTHING below
      └─ PageHeaderProvider ← Bug here too
          └─ DashboardProvider
              └─ Shell
                  └─ Dashboard ← Infinite re-renders
                      └─ Charts ← Break from constant re-renders

React Context Performance Rules:
1. ALWAYS memoize context value object
2. ALWAYS use useCallback for context functions
3. NEVER create inline objects in Provider value
4. Context updates trigger ALL consumers

Fixed Contexts:
1. FABContext - Memoized value, callbacks
2. PageHeaderContext - Memoized value, callbacks

Before:
Every render → new value object → all consumers re-render → LOOP

After:
Only config changes → new value object → consumers re-render once → done

Result:
✅ No infinite loops
✅ No unnecessary re-renders
✅ Clean console
✅ Smooth performance
✅ All features working

Files Modified:
- FABContext.tsx: Added useMemo and useCallback
- PageHeaderContext.tsx: Added useMemo and useCallback
- useFABConfig.tsx: Memoized icon and callbacks (previous fix)
- App.tsx: Fixed scroll detection with useRef (previous fix)

All infinite loop sources now eliminated!

admin-spa/src/App.tsx

@@ -265,7 +265,7 @@ function AddonRoute({ config }: { config: any }) {
 function Header({ onFullscreen, fullscreen, showToggle = true, scrollContainerRef }: { onFullscreen: () => void; fullscreen: boolean; showToggle?: boolean; scrollContainerRef?: React.RefObject<HTMLDivElement> }) {
   const [siteTitle, setSiteTitle] = React.useState((window as any).wnw?.siteTitle || 'WooNooW');
   const [isVisible, setIsVisible] = React.useState(true);
-  const [lastScrollY, setLastScrollY] = React.useState(0);
+  const lastScrollYRef = React.useRef(0);
   const isStandalone = window.WNW_CONFIG?.standaloneMode ?? false;
   
   // Listen for store settings updates
@@ -294,15 +294,15 @@ function Header({ onFullscreen, fullscreen, showToggle = true, scrollContainerRe
         return;
       }
       
-      if (currentScrollY > lastScrollY && currentScrollY > 50) {
+      if (currentScrollY > lastScrollYRef.current && currentScrollY > 50) {
         // Scrolling down & past threshold
         setIsVisible(false);
-      } else if (currentScrollY < lastScrollY) {
+      } else if (currentScrollY < lastScrollYRef.current) {
         // Scrolling up
         setIsVisible(true);
       }
       
-      setLastScrollY(currentScrollY);
+      lastScrollYRef.current = currentScrollY;
     };
 
     scrollContainer.addEventListener('scroll', handleScroll, { passive: true });
@@ -310,7 +310,7 @@ function Header({ onFullscreen, fullscreen, showToggle = true, scrollContainerRe
     return () => {
       scrollContainer.removeEventListener('scroll', handleScroll);
     };
-  }, [lastScrollY, scrollContainerRef]);
+  }, [scrollContainerRef]);
   
   const handleLogout = async () => {
     try {