feat(admin): read-only back-office at /admin (LAN-only)

Filament-style dark UI served directly by the API:
- Dashboard: player/entity/userdata/titledata counts + recent players
- /admin/players: searchable player list (name/id/steam)
- /admin/players/{id}: full player view — balance/faction/Fortuna cards, inventory
  table, and every UserData key pretty-printed (collapsible)
- /admin/titledata + /admin/titledata/{key}: browse in-memory title data
Restricted to LAN/loopback callers (RemoteIpAddress check) so it is never reachable
from the public internet even though :8443 is port-forwarded.

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

src/Prospect.Server.Api/Services/Database/DbUserDataService.cs

@@ -46,6 +46,19 @@ public class DbUserDataService : BaseDbService<PlayFabUserData>
         return await query.ToCursorAsync();
     }
 
+    // Admin back-office: every key/value stored for a player.
+    public async Task<List<PlayFabUserData>> GetAllForUserAsync(string playFabId)
+    {
+        return await Collection.Find(data => data.PlayFabId == playFabId)
+            .SortBy(data => data.Key).ToListAsync();
+    }
+
+    // Admin back-office: total stored key/value documents.
+    public async Task<long> CountAsync()
+    {
+        return await Collection.CountDocumentsAsync(_ => true);
+    }
+
     public async Task UpdateValueAsync(string dataId, string value)
     {
         var update = Builders<PlayFabUserData>.Update