Stage 17 round 5 — backend/correctness bug fixes

- Resign on the opponent's turn: engine ResignSeat(seat) resigns a specific seat
  (not just toMove); game.Resign bypasses the turn check and forfeits the actor's seat.
- Quick-match cancel was a UI no-op (only stopped polling): add the full path
  (REST /lobby/cancel -> gateway lobby.cancel -> client) and clear the matchmaker's
  pending result on Cancel, so a cancelled search is dequeued (no 'already queued', no
  later robot-substituted game). NewGame dequeues on cancel and on abandon.
- Lobby win/loss: result.ts ranked by score, so a 0-0 resignation read as a win.
  The winner now takes rank 1 and the viewer is placed from rank 2 — matching the
  game-detail screen.
- Friend request to a robot: robots no longer block requests; the request stays
  pending and expires (friendRequestTTL), mirroring a human who ignores it.
- Nudge cooldown: ErrNudgeTooSoon now maps to a distinct nudge_too_soon code with a
  correct message; the chat nudge button disables during the hourly cooldown; the
  nudge note reads 'Waiting for your move!' (button keeps the Nudge action label).
Tests: engine/service off-turn resign, matchmaker cancel-clears-result, friend-to-robot
inttest, result.ts 0-0 resignation, nudge_too_soon mapping.

backend/internal/inttest/social_test.go

@@ -40,6 +40,38 @@ func newGameWithSeats(t *testing.T, n int) (uuid.UUID, []uuid.UUID) {
 	return g.ID, seats
 }
 
+// TestFriendRequestToRobotStaysPending checks a friend request to a robot is accepted as
+// pending rather than blocked: robots no longer block friend requests, so the request
+// just sits unanswered and later expires — mirroring a human who ignores it (Stage 17).
+func TestFriendRequestToRobotStaysPending(t *testing.T) {
+	ctx := context.Background()
+	svc := newSocialService()
+	accs := account.NewStore(testDB)
+
+	human := provisionAccount(t)
+	robot, err := accs.ProvisionRobot(ctx, "robot-friend-"+uuid.NewString(), "Robbie")
+	if err != nil {
+		t.Fatalf("provision robot: %v", err)
+	}
+	if robot.BlockFriendRequests {
+		t.Fatal("robot must not block friend requests")
+	}
+	// A request is only allowed between players who share a game.
+	if _, err := newGameService().Create(ctx, game.CreateParams{
+		Variant: engine.VariantEnglish, Seats: []uuid.UUID{human, robot.ID},
+		TurnTimeout: 24 * time.Hour, Seed: openingSeed(t),
+	}); err != nil {
+		t.Fatalf("create game: %v", err)
+	}
+
+	if err := svc.SendFriendRequest(ctx, human, robot.ID); err != nil {
+		t.Fatalf("request to robot = %v, want nil (accepted as pending)", err)
+	}
+	if got, _ := svc.ListIncomingRequests(ctx, robot.ID); len(got) != 1 || got[0] != human {
+		t.Fatalf("robot incoming = %v, want [human]", got)
+	}
+}
+
 func TestFriendRequestLifecycle(t *testing.T) {
 	ctx := context.Background()
 	svc := newSocialService()