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>

backend/migrations/013_loot_profiles.sql

@@ -0,0 +1,13 @@
+-- Loot profiles for BetterLoot integration
+CREATE TABLE loot_profiles (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    license_id UUID NOT NULL REFERENCES licenses(id) ON DELETE CASCADE,
+    profile_name VARCHAR(100) NOT NULL,
+    description TEXT,
+    loot_table JSONB NOT NULL DEFAULT '{}',
+    loot_groups JSONB NOT NULL DEFAULT '{}',
+    is_active BOOLEAN NOT NULL DEFAULT false,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+CREATE INDEX idx_loot_profiles_license ON loot_profiles(license_id);