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/AdminPaymentMethodEdit.tsx

@@ -7,33 +7,7 @@ import { METHOD_LABELS } from '../constants/paymentMethods';
 import type { PromoGroupSimple } from '../types';
 import { usePlatform } from '../platform/hooks/usePlatform';
 import { createNumberInputHandler, toNumber } from '../utils/inputHelpers';
-const BackIcon = () => (
-  <svg
-    className="h-5 w-5 text-dark-400"
-    fill="none"
-    viewBox="0 0 24 24"
-    stroke="currentColor"
-    strokeWidth={2}
-  >
-    <path strokeLinecap="round" strokeLinejoin="round" d="M15.75 19.5L8.25 12l7.5-7.5" />
-  </svg>
-);
-
-const CheckIcon = () => (
-  <svg className="h-4 w-4" fill="none" viewBox="0 0 24 24" stroke="currentColor" strokeWidth={2}>
-    <path strokeLinecap="round" strokeLinejoin="round" d="M4.5 12.75l6 6 9-13.5" />
-  </svg>
-);
-
-const SaveIcon = () => (
-  <svg className="h-4 w-4" fill="none" viewBox="0 0 24 24" stroke="currentColor" strokeWidth={2}>
-    <path
-      strokeLinecap="round"
-      strokeLinejoin="round"
-      d="M3 16.5v2.25A2.25 2.25 0 005.25 21h13.5A2.25 2.25 0 0021 18.75V16.5M16.5 12L12 16.5m0 0L7.5 12m4.5 4.5V3"
-    />
-  </svg>
-);
+import { BackIcon, CheckIcon, SaveIcon } from '@/components/icons';
 
 export default function AdminPaymentMethodEdit() {
   const { t } = useTranslation();
@@ -462,7 +436,7 @@ export default function AdminPaymentMethodEdit() {
           {updateMethodMutation.isPending ? (
             <div className="h-4 w-4 animate-spin rounded-full border-2 border-white/30 border-t-white" />
           ) : (
-            <SaveIcon />
+            <SaveIcon className="h-4 w-4" />
           )}
           {t('admin.paymentMethods.saveButton')}
         </button>