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/AIOnboarding.tsx

@@ -320,7 +320,7 @@ export default function AIOnboarding({ onCancel, onComplete, categories, invento
                </div>
             </div>
             
-            <div className="absolute top-6 left-1/2 -translate-x-1/2 bg-black/60 backdrop-blur-md px-4 py-1.5 rounded-full border border-white/10">
+            <div className="absolute top-6 left-1/2 -translate-x-1/2 bg-black/60 px-4 py-1.5 rounded-full border border-white/10">
                <span className="text-xs font-black text-white flex items-center gap-2">
                  <div className="w-1.5 h-1.5 rounded-full bg-red-500 animate-pulse" />
                  Live Viewfinder
@@ -353,7 +353,7 @@ export default function AIOnboarding({ onCancel, onComplete, categories, invento
             <div className="absolute inset-0 bg-gradient-to-t from-black/60 via-transparent to-transparent pointer-events-none" />
             
             {uploading && (
-              <div className="absolute inset-0 bg-slate-950/60 backdrop-blur-sm flex flex-col items-center justify-center gap-4 z-10 transition-all">
+              <div className="absolute inset-0 bg-slate-950/60 flex flex-col items-center justify-center gap-4 z-10 transition-all">
                 <div className="relative">
                   <RefreshCw className="w-12 h-12 text-primary animate-spin" />
                   <Sparkles className="absolute -top-2 -right-2 text-amber-400 w-6 h-6 animate-pulse" />