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/app/page.tsx

@@ -470,7 +470,7 @@ export default function Home() {
 
         <div className="w-full px-1 space-y-6">
           {/* Mode Switcher */}
-          <div className="flex p-1.5 bg-slate-900/80 backdrop-blur-md rounded-2xl shadow-inner w-full gap-1">
+          <div className="flex p-1.5 bg-slate-900/80 rounded-2xl shadow-inner w-full gap-1">
             {[
               { id: 'CHECK_IN', label: 'Check In', icon: ArrowDownCircle },
               { id: 'CHECK_OUT', label: 'Check Out', icon: ArrowUpCircle },
@@ -545,7 +545,7 @@ export default function Home() {
 
         {/* Stock Adjustment Overlay */}
         {selectedItem && (
-          <div className="fixed inset-0 z-50 flex items-end sm:items-center justify-center p-4 bg-slate-950/80 backdrop-blur-sm animate-in fade-in duration-200">
+          <div className="fixed inset-0 z-50 flex items-end sm:items-center justify-center p-4 bg-slate-950/80 animate-in fade-in duration-200">
             <div className="w-full max-w-lg bg-slate-900 border border-slate-800 rounded-[2.5rem] shadow-2xl p-6 overflow-hidden animate-in slide-in-from-bottom-10 duration-300">
               <div className="flex justify-between items-center mb-6">
                 <h3 className="text-xl font-black tracking-tight flex items-center gap-2">
@@ -806,7 +806,7 @@ export default function Home() {
 
         {/* Box Contents Selection Modal */}
       {boxMatches.length > 0 && !selectedItem && (
-        <div className="fixed inset-0 z-50 flex items-end sm:items-center justify-center p-4 bg-slate-950/80 backdrop-blur-sm animate-in fade-in duration-200">
+        <div className="fixed inset-0 z-50 flex items-end sm:items-center justify-center p-4 bg-slate-950/80 animate-in fade-in duration-200">
           <div className="w-full max-w-lg bg-slate-900 border border-slate-800 rounded-[2.5rem] shadow-2xl p-6 overflow-hidden animate-in slide-in-from-bottom-10 duration-300 flex flex-col max-h-[85vh]">
             <div className="flex justify-between items-center mb-6 shrink-0">
               <div>