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/components/dashboard/StatsGrid.tsx

@@ -1,3 +1,4 @@
+import { PiCaretRightDuotone } from 'react-icons/pi';
 import { useTranslation } from 'react-i18next';
 import { Link } from 'react-router';
 import { useCurrency } from '../../hooks/useCurrency';
@@ -12,22 +13,7 @@ interface StatsGridProps {
 }
 
 const ChevronIcon = ({ color }: { color: string }) => (
-  <svg
-    width="16"
-    height="16"
-    viewBox="0 0 16 16"
-    fill="none"
-    style={{ flexShrink: 0 }}
-    aria-hidden="true"
-  >
-    <path
-      d="M6 4l4 4-4 4"
-      stroke={color}
-      strokeWidth="1.5"
-      strokeLinecap="round"
-      strokeLinejoin="round"
-    />
-  </svg>
+  <PiCaretRightDuotone width={16} height={16} style={{ flexShrink: 0, color }} aria-hidden="true" />
 );
 
 export default function StatsGrid({