feat: transform UI to dark cyberpunk theme

- Eliminate all white/light boxes and backgrounds
- Fix drag-drop zone with neon cyberpunk colors (#00f0ff, #ff006e, #16213e)
- Fix restored mnemonic display with matrix green (#39ff14)
- Fix security options panel with dark gradient
- Fix all remaining slate-700/slate-800 labels to cyberpunk neon
- Fix info banners and text colors
- Update badge components with cyberpunk color scheme
- Apply consistent dark theme across all components

src/components/SecurityWarnings.tsx

@@ -39,8 +39,8 @@ export const SecurityWarnings: React.FC = () => {
                 description="If hosted online: DNS, HTTPS, CDN, and browser can see usage patterns. Use offline/local for maximum security."
             />
 
-            <div className="pt-3 border-t border-slate-600 text-xs text-slate-400">
-                <strong className="text-slate-300">Recommendation:</strong>{' '}
+            <div className="pt-3 border-t border-[#00f0ff]/30 text-xs text-[#6ef3f7]">
+                <strong className="text-[#00f0ff]">Recommendation:</strong>{' '}
                 Use this tool on a dedicated offline device. Clear browser data after each use. Never use on shared/public computers.
             </div>
         </div>
@@ -59,8 +59,8 @@ const Warning = ({
     <div className="flex gap-2 text-sm">
         <span className="text-lg flex-shrink-0">{icon}</span>
         <div>
-            <div className="font-semibold text-slate-200 mb-1">{title}</div>
-            <div className="text-slate-400 leading-relaxed">{description}</div>
+            <div className="font-semibold text-[#00f0ff] mb-1" style={{ textShadow: '0 0 10px rgba(0,240,255,0.7)' }}>{title}</div>
+            <div className="text-[#6ef3f7] leading-relaxed">{description}</div>
         </div>
     </div>
 );