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/BottomNav.tsx

@@ -25,7 +25,7 @@ export default function BottomNav({
   const isAdmin = pathname === '/admin';
 
   return (
-    <footer className="fixed bottom-0 left-0 right-0 py-3 px-2 pb-safe bg-slate-950/80 backdrop-blur-lg border-t border-slate-900/50 z-40 transition-all duration-300">
+    <footer className="fixed bottom-0 left-0 right-0 py-3 px-2 pb-safe bg-slate-950 border-t border-slate-900 z-40 transition-all duration-300">
       <div className="max-w-xl mx-auto flex justify-around items-center text-slate-400">
         
         <button