feat: Add file manager view using VueFinder

Installs VueFinder and wires it to the backend /api/files endpoint with
JWT Bearer auth. Adds /files route, File Manager nav item (files.view
permission-gated, FolderOpen icon), and imports VueFinder CSS globally.
Driver token is computed reactively so it tracks token refreshes automatically.
Uses midnight theme to match the dark admin panel aesthetic.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/components/layout/DashboardLayout.vue

@@ -26,6 +26,7 @@ import {
   Clock,
   AlertTriangle,
   FileText,
+  FolderOpen,
   Menu,
   X,
 } from 'lucide-vue-next'
@@ -42,6 +43,7 @@ const navItems = [
   { name: 'Console', path: '/console', icon: Terminal, permission: 'console.view' },
   { name: 'Players', path: '/players', icon: Users, permission: 'players.view' },
   { name: 'Plugins', path: '/plugins', icon: Puzzle, permission: 'plugins.view' },
+  { name: 'File Manager', path: '/files', icon: FolderOpen, permission: 'files.view' },
   { name: 'Auto-Wiper', path: '/wipes', icon: RefreshCw, permission: 'wipes.view' },
   { name: 'Maps', path: '/maps', icon: Map, permission: 'maps.view' },
   { name: 'Chat Log', path: '/chat', icon: MessageSquare, permission: 'chat.view' },