feat(cabinet): migrate all icons to the panel's Phosphor set

Replace the cabinet's hand-written heroicons-style SVG icon components with
the Remnawave panel's own icon family — Phosphor via react-icons/pi (Duotone).
All icons now live in a single central barrel (src/components/icons:
index + extended-icons + editor-icons, 144 icons); every feature file imports
from it instead of redefining inline SVGs (~440 icon defs removed).

- Add react-icons dependency
- Desktop nav (AppShell) now uses the central Phosphor icons, removing a
  stroke-vs-duotone inconsistency the partial migration introduced
- Icons with custom props (SortIcon's direction, expandable chevrons) kept as
  thin Phosphor wrappers; the RemnawaveIcon brand logo and animated SVGs
  (checkmarks, spinners) are intentionally left as-is
- Restore the original per-call-site icon sizes wherever the centralized
  default differed (211 call sites)

src/pages/AdminPromocodeStats.tsx

@@ -4,37 +4,7 @@ import { useTranslation } from 'react-i18next';
 import i18n from '../i18n';
 import { promocodesApi, PromoCodeType } from '../api/promocodes';
 import { AdminBackButton } from '../components/admin';
-
-// Icons
-const EditIcon = () => (
-  <svg className="h-4 w-4" fill="none" viewBox="0 0 24 24" stroke="currentColor" strokeWidth={2}>
-    <path
-      strokeLinecap="round"
-      strokeLinejoin="round"
-      d="M16.862 4.487l1.687-1.688a1.875 1.875 0 112.652 2.652L10.582 16.07a4.5 4.5 0 01-1.897 1.13L6 18l.8-2.685a4.5 4.5 0 011.13-1.897l8.932-8.931zm0 0L19.5 7.125M18 14v4.75A2.25 2.25 0 0115.75 21H5.25A2.25 2.25 0 013 18.75V8.25A2.25 2.25 0 015.25 6H10"
-    />
-  </svg>
-);
-
-const ClockIcon = () => (
-  <svg className="h-4 w-4" fill="none" viewBox="0 0 24 24" stroke="currentColor" strokeWidth={2}>
-    <path
-      strokeLinecap="round"
-      strokeLinejoin="round"
-      d="M12 6v6h4.5m4.5 0a9 9 0 11-18 0 9 9 0 0118 0z"
-    />
-  </svg>
-);
-
-const UserIcon = () => (
-  <svg className="h-4 w-4" fill="none" viewBox="0 0 24 24" stroke="currentColor" strokeWidth={2}>
-    <path
-      strokeLinecap="round"
-      strokeLinejoin="round"
-      d="M15.75 6a3.75 3.75 0 11-7.5 0 3.75 3.75 0 017.5 0zM4.501 20.118a7.5 7.5 0 0114.998 0A17.933 17.933 0 0112 21.75c-2.676 0-5.216-.584-7.499-1.632z"
-    />
-  </svg>
-);
+import { EditIcon, ClockIcon, UserIcon } from '@/components/icons';
 
 // Helper functions
 const getTypeLabel = (type: PromoCodeType): string => {
@@ -253,7 +223,7 @@ export default function AdminPromocodeStats() {
         {/* Usage History */}
         <div className="rounded-xl border border-dark-700 bg-dark-800 p-4">
           <h4 className="mb-4 flex items-center gap-2 font-medium text-dark-200">
-            <ClockIcon />
+            <ClockIcon className="h-4 w-4" />
             {t('admin.promocodes.stats.usageHistory')}
           </h4>
           {promocode.recent_uses.length === 0 ? (
@@ -269,7 +239,7 @@ export default function AdminPromocodeStats() {
                 >
                   <div className="flex items-center gap-3">
                     <div className="flex h-8 w-8 shrink-0 items-center justify-center rounded-full bg-dark-500">
-                      <UserIcon />
+                      <UserIcon className="h-4 w-4" />
                     </div>
                     <div className="min-w-0">
                       <div className="truncate text-sm font-medium text-dark-200">