feat: Add loot builder frontend — Pinia store, views, 4 components, router + nav

Implements the complete frontend for BetterLoot profile management:
- Pinia store (loot.ts) with CRUD, import/export, apply-to-server actions
- LootBuilderView orchestrator with profile bar, modals, two-column layout
- LootContainerSidebar with categorized container list, search, config indicators
- LootItemEditor for per-container item settings and ungrouped item table
- LootItemPicker modal with searchable/filterable Rust item grid
- LootGroupEditor for reusable loot group management
- Router integration at /loot-builder
- Sidebar nav item with Crosshair icon and loot.view permission

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

frontend/src/router/index.ts

@@ -110,6 +110,11 @@ const panelRoutes: RouteRecordRaw[] = [
         name: 'files',
         component: () => import('@/views/admin/FileManagerView.vue'),
       },
+      {
+        path: 'loot-builder',
+        name: 'loot-builder',
+        component: () => import('@/views/admin/LootBuilderView.vue'),
+      },
       {
         path: 'wipes',
         name: 'wipes',