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/admin/DatabaseManager.tsx

@@ -35,7 +35,7 @@ export default function DatabaseManager({
 
   return (
     <div className="space-y-6 md:space-y-8 h-full">
-      <div className="bg-slate-900/40 backdrop-blur-xl border border-slate-800/50 rounded-[2.5rem] p-5 md:p-8 shadow-2xl overflow-hidden relative group transition-all">
+      <div className="bg-slate-900/40 border border-slate-800/50 rounded-[2.5rem] p-5 md:p-8 shadow-2xl overflow-hidden relative group transition-all">
         <div className="flex items-center gap-4 mb-6">
           <div className="w-10 h-10 rounded-xl bg-indigo-500/10 flex items-center justify-center text-indigo-400 border border-indigo-500/20">
             <Database size={20} />
@@ -68,7 +68,7 @@ export default function DatabaseManager({
         </div>
       </div>
 
-      <div className="bg-slate-900/40 backdrop-blur-xl border border-slate-800/50 rounded-[2.5rem] p-5 md:p-8 shadow-2xl space-y-8">
+      <div className="bg-slate-900/40 border border-slate-800/50 rounded-[2.5rem] p-5 md:p-8 shadow-2xl space-y-8">
         <div className="space-y-6">
           <div className="flex items-center gap-4">
              <div className="w-10 h-10 rounded-xl bg-indigo-500/10 flex items-center justify-center text-indigo-400 border border-indigo-500/20">