feat: Add loot builder backend + static data + DB migration

- Migration 013: loot_profiles table (JSONB loot_table + loot_groups, license-scoped)
- TypeORM entity matching migration schema exactly
- NestJS loot module: 10 endpoints (CRUD, duplicate, apply, import, export, containers)
- Multiplier logic recursively scales Min/Max/Scrap across loot tables and groups
- Apply-to-server writes BetterLoot JSON via NATS file manager + RCON reload
- Frontend static data: 191 Rust items, 51 container prefabs
- TypeScript types for BetterLoot data model (PrefabLoot, LootEntry, LootRNG, etc.)
- Fix vue-tsc errors: UngroupedItems uses LootRNG, null safety in store/view

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

frontend/src/views/admin/LootBuilderView.vue

@@ -26,7 +26,7 @@ const multipliers = [1, 2, 5, 10]
 
 onMounted(async () => {
   await loot.fetchProfiles()
-  if (loot.profiles.length > 0) {
+  if (loot.profiles.length > 0 && loot.profiles[0]) {
     await loot.loadProfile(loot.profiles[0].id)
   }
 })
@@ -110,7 +110,7 @@ function handleAddItem(shortname: string) {
       ItemSettings: { ItemsMin: 1, ItemsMax: 6, MinScrap: 0, MaxScrap: 0 },
     }
   }
-  const container = table[loot.selectedContainer]
+  const container = table[loot.selectedContainer]!
   if (!container.UngroupedItems) container.UngroupedItems = {}
   if (!container.UngroupedItems[shortname]) {
     container.UngroupedItems[shortname] = {