feat: resolve player display names from Steam persona (Steam Web API)

Accounts were created as 'Unknown' and the client never sends a name, so the admin
panel / friends / squad showed no names. Add SteamWebApiService (GetPlayerSummaries),
wired into LoginWithSteam to backfill the DisplayName from the Steam persona when it's
still 'Unknown'. Admin gets a LAN-only /admin/backfill-names action (+ button) to
backfill existing accounts in one shot. Key read from config SteamWebApiKey (Vault ->
env), inert when unset.

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

src/Prospect.Server.Api/Controllers/ClientController.cs

@@ -32,6 +32,7 @@ public class ClientController : Controller
     private readonly DbEntityService _entityService;
     private readonly UserDataService _userDataService;
     private readonly TitleDataService _titleDataService;
+    private readonly Prospect.Server.Api.Services.Steam.SteamWebApiService _steamWebApi;
 
     public ClientController(ILogger<ClientController> logger,
         IOptions<PlayFabSettings> settings,
@@ -39,7 +40,8 @@ public class ClientController : Controller
         DbUserService userService,
         DbEntityService entityService,
         UserDataService userDataService,
-        TitleDataService titleDataService)
+        TitleDataService titleDataService,
+        Prospect.Server.Api.Services.Steam.SteamWebApiService steamWebApi)
     {
         _settings = settings.Value;
         _logger = logger;
@@ -48,6 +50,7 @@ public class ClientController : Controller
         _entityService = entityService;
         _userDataService = userDataService;
         _titleDataService = titleDataService;
+        _steamWebApi = steamWebApi;
     }
 
     [AllowAnonymous]
@@ -63,6 +66,19 @@ public class ClientController : Controller
                 var userSteamId = ticket.SteamId.ToString();
 
                 var user = await _userService.FindOrCreateAsync(PlayFabUserAuthType.Steam, userSteamId);
+
+                // Backfill the display name from the Steam persona when we don't have a real
+                // one yet (accounts are created as "Unknown"; the client never sends a name).
+                if (string.IsNullOrEmpty(user.DisplayName) || user.DisplayName == "Unknown")
+                {
+                    var persona = await _steamWebApi.GetPersonaNameAsync(userSteamId);
+                    if (!string.IsNullOrWhiteSpace(persona))
+                    {
+                        await _userService.UpdateDisplayNameAsync(user.Id, persona);
+                        user.DisplayName = persona;
+                    }
+                }
+
                 var entity = await _entityService.FindOrCreateAsync(user.Id);
 
                 var userTicket = _authTokenService.GenerateUser(entity);