refactor(frontend): eliminate backdrop-blur throughout codebase

Remove all instances of backdrop-blur effect (14+ occurrences) to simplify visual design
and eliminate signature 2023-2024 AI aesthetic tell. Components now use solid backgrounds
and borders for hierarchy and affordance instead of decorative blur.

Affected:
- BottomNav: solid bg-slate-950, clean border
- AdminOverlay: removed overlay blur
- Admin managers (Identity, Database, AI, Category, LDAP): removed glass-card aesthetic
- Modals (IdentityCheck, Scanner, AIOnboarding): removed decorative blur
- Page layouts (home, inventory, logs): removed modal backdrop blur
- globals.css: removed glass-card utility

Build: passes with zero errors. Bundle sizes unchanged.

Simplification improves: clarity, perceived intentionality, removes AI aesthetic tells.

frontend/components/IdentityCheckOverlay.tsx

@@ -60,7 +60,7 @@ const IdentityCheckOverlay = memo(({ show, users, onAuthenticated }: IdentityChe
   };
 
   return (
-    <div className="fixed inset-0 z-[100] flex items-center justify-center p-4 bg-slate-950/90 backdrop-blur-2xl animate-in fade-in duration-500">
+    <div className="fixed inset-0 z-[100] flex items-center justify-center p-4 bg-slate-950/90 animate-in fade-in duration-500">
       <div className="bg-slate-900/80 border border-slate-800 rounded-[2.5rem] p-8 sm:p-10 max-w-sm w-full shadow-2xl space-y-8 animate-in zoom-in-95 duration-300 relative overflow-hidden">
         {/* Subtle accent light */}
         <div className="absolute top-0 left-1/2 -translate-x-1/2 w-40 h-1 bg-gradient-to-r from-transparent via-primary/50 to-transparent blur-sm" />