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/connection/blocks/BlockButtons.tsx

@@ -1,5 +1,6 @@
 import { useState, useCallback } from 'react';
 import { useTranslation } from 'react-i18next';
+import { CheckIcon, CopyIcon } from '@/components/icons';
 import type { RemnawaveButtonClient, LocalizedText } from '@/types';
 import { copyToClipboard } from '@/utils/clipboard';
 
@@ -20,22 +21,6 @@ function isValidExternalUrl(url: string | undefined): boolean {
   return lowerUrl.startsWith('http://') || lowerUrl.startsWith('https://');
 }
 
-const CopyIcon = () => (
-  <svg className="h-4 w-4" fill="none" viewBox="0 0 24 24" stroke="currentColor" strokeWidth={1.5}>
-    <path
-      strokeLinecap="round"
-      strokeLinejoin="round"
-      d="M8 16H6a2 2 0 01-2-2V6a2 2 0 012-2h8a2 2 0 012 2v2m-6 12h8a2 2 0 002-2v-8a2 2 0 00-2-2h-8a2 2 0 00-2 2v8a2 2 0 002 2z"
-    />
-  </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="M5 13l4 4L19 7" />
-  </svg>
-);
-
 interface BlockButtonsProps {
   buttons: RemnawaveButtonClient[] | undefined;
   variant: 'light' | 'subtle';