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/AiManager.tsx

@@ -32,7 +32,7 @@ export default function AiManager({
   onUpdatePrompt
 }: AiManagerProps) {
   return (
-    <section 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-6 transition-all group/ai">
+    <section className="bg-slate-900/40 border border-slate-800/50 rounded-[2.5rem] p-5 md:p-8 shadow-2xl space-y-6 transition-all group/ai">
       <div className="flex items-center justify-between mb-2">
         <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">