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/CategoryManager.tsx

@@ -23,7 +23,7 @@ export default function CategoryManager({
   onUpdateCategorySubmit
 }: CategoryManagerProps) {
   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/categories">
+    <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/categories">
       <div className="flex items-center justify-between px-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">
@@ -69,7 +69,7 @@ export default function CategoryManager({
 
       {/* Edit Category Modal */}
       {editingCategory && (
-        <div className="fixed inset-0 z-[100] flex items-end sm:items-center justify-center p-0 sm:p-4 bg-slate-950/90 backdrop-blur-xl animate-in fade-in duration-300">
+        <div className="fixed inset-0 z-[100] flex items-end sm:items-center justify-center p-0 sm:p-4 bg-slate-950/90 animate-in fade-in duration-300">
           <div className="w-full max-w-lg bg-slate-900 border-x border-t sm:border border-slate-800 rounded-t-[2.5rem] sm:rounded-3xl p-6 sm:p-10 shadow-2xl space-y-8 overflow-hidden animate-in slide-in-from-bottom-10">
             <div className="flex justify-between items-center">
                <div className="flex items-center gap-4">