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/AdminController.cs

@@ -4,6 +4,8 @@ using System.Text;
 using System.Text.Json;
 using Microsoft.AspNetCore.Mvc;
 using Prospect.Server.Api.Services.Database;
+using Prospect.Server.Api.Services.Database.Models;
+using Prospect.Server.Api.Services.Steam;
 using Prospect.Server.Api.Services.UserData;
 
 namespace Prospect.Server.Api.Controllers;
@@ -18,14 +20,16 @@ public class AdminController : ControllerBase
     private readonly DbEntityService _entityService;
     private readonly DbUserDataService _userDataService;
     private readonly TitleDataService _titleDataService;
+    private readonly SteamWebApiService _steamWebApi;
 
     public AdminController(DbUserService userService, DbEntityService entityService,
-        DbUserDataService userDataService, TitleDataService titleDataService)
+        DbUserDataService userDataService, TitleDataService titleDataService, SteamWebApiService steamWebApi)
     {
         _userService = userService;
         _entityService = entityService;
         _userDataService = userDataService;
         _titleDataService = titleDataService;
+        _steamWebApi = steamWebApi;
     }
 
     // ---------- pages ----------
@@ -82,7 +86,8 @@ public class AdminController : ControllerBase
         }
 
         var sb = new StringBuilder();
-        sb.Append($"<form method='get' class='search'><input name='q' placeholder='Rechercher nom / id / steam…' value='{Esc(q ?? "")}'/><button class='btn'>Rechercher</button></form>");
+        sb.Append($"<form method='get' class='search'><input name='q' placeholder='Rechercher nom / id / steam…' value='{Esc(q ?? "")}'/><button class='btn'>Rechercher</button>" +
+                  "<a class='btn' href='/admin/backfill-names' title='Récupère les pseudos Steam des comptes sans nom'>Backfill pseudos Steam</a></form>");
         sb.Append($"<p class='muted'>{users.Count} joueur(s)</p>");
         sb.Append("<table><thead><tr><th>DisplayName</th><th>PlayFab Id</th><th>Entity Id</th><th>Auth</th><th></th></tr></thead><tbody>");
         foreach (var u in users.OrderBy(u => u.DisplayName))
@@ -179,6 +184,38 @@ public class AdminController : ControllerBase
         return Html(Layout("TitleData · " + key, $"<h2 class='mono'>{Esc(key)}</h2>" + body));
     }
 
+    [HttpGet("backfill-names")]
+    public async Task<IActionResult> BackfillNames()
+    {
+        if (!IsLan()) return Denied();
+        if (!_steamWebApi.Enabled)
+            return Html(Layout("Backfill", "<p class='muted'>Steam Web API non configurée (clé absente).</p><p><a class='btn' href='/admin/players'>← Joueurs</a></p>"));
+
+        var users = await _userService.GetAllAsync();
+        int updated = 0, skipped = 0, failed = 0;
+        var rows = new StringBuilder();
+        foreach (var u in users)
+        {
+            if (!string.IsNullOrEmpty(u.DisplayName) && u.DisplayName != "Unknown") { skipped++; continue; }
+            var steam = u.Auth?.FirstOrDefault(a => a.Type == PlayFabUserAuthType.Steam)?.Key;
+            if (string.IsNullOrEmpty(steam)) { skipped++; continue; }
+
+            var persona = await _steamWebApi.GetPersonaNameAsync(steam);
+            if (!string.IsNullOrWhiteSpace(persona))
+            {
+                await _userService.UpdateDisplayNameAsync(u.Id, persona);
+                updated++;
+                rows.Append($"<tr><td class='mono small'>{Esc(u.Id)}</td><td>{Esc(persona)}</td></tr>");
+            }
+            else { failed++; }
+        }
+
+        var body = $"<h2>Backfill des pseudos Steam</h2><p class='muted'>{updated} mis à jour · {skipped} ignorés · {failed} échec(s)</p>" +
+                   (updated > 0 ? $"<table><thead><tr><th>PlayFabId</th><th>Nouveau nom</th></tr></thead><tbody>{rows}</tbody></table>" : "") +
+                   "<p><a class='btn' href='/admin/players'>← Joueurs</a></p>";
+        return Html(Layout("Backfill", body));
+    }
+
     // ---------- helpers ----------
 
     private bool IsLan()