feat(admin): resolve item/vanity ids to readable names + catalog browser

Bundle a compact id -> {name,rarity,category} lookup (Data/gameref.json, 1177 entries,
built from community-datamined TCF-Wiki data) and a GameRefService. The admin back-office
now shows readable names + coloured rarity for inventory items instead of raw ids, and a
new /admin/catalog page browses the known game catalog (searchable, by category).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/Prospect.Server.Api/Startup.cs

@@ -31,6 +31,7 @@ public class Startup
         services.AddSingleton<TitleDataService>();
 
         services.AddSingleton<Prospect.Server.Api.Services.Steam.SteamWebApiService>();
+        services.AddSingleton<Prospect.Server.Api.Services.GameRef.GameRefService>();
 
         services.AddSingleton<DbUserService>();
         services.AddSingleton<DbEntityService>();