Add player onboarding and tactical viewer updates

apps/backend/PlayerFaction/Api/CompletePlayerOnboardingHandler.cs

@@ -0,0 +1,31 @@
+using FastEndpoints;
+
+namespace SpaceGame.Api.PlayerFaction.Api;
+
+public sealed class CompletePlayerOnboardingHandler(WorldService worldService) : Endpoint<CompletePlayerOnboardingRequest, PlayerFactionSnapshot>
+{
+    public override void Configure()
+    {
+        Post("/api/player-faction/onboarding");
+    }
+
+    public override async Task HandleAsync(CompletePlayerOnboardingRequest request, CancellationToken cancellationToken)
+    {
+        try
+        {
+            var snapshot = worldService.CompletePlayerOnboarding(request);
+            if (snapshot is null)
+            {
+                await SendNotFoundAsync(cancellationToken);
+                return;
+            }
+
+            await SendOkAsync(snapshot, cancellationToken);
+        }
+        catch (InvalidOperationException ex)
+        {
+            AddError(ex.Message);
+            await SendErrorsAsync(cancellation: cancellationToken);
+        }
+    }
+}