Add participant creation functionality to event API, including backend service and database integration. Update frontend to support participant registration and enhance UI for displaying registered players.

backend/internal/application/service.go

@@ -5,6 +5,7 @@ import (
 	"crypto/rand"
 	"encoding/hex"
 	"fmt"
+	"strings"
 	"time"
 
 	"mixmaker/backend/internal/domain"
@@ -18,6 +19,7 @@ type Store interface {
 	DeleteSession(context.Context, string) error
 	UpdatePlayer(context.Context, domain.Player) (domain.Player, error)
 	ListPlayers(context.Context) ([]domain.Player, error)
+	CreateParticipant(context.Context, domain.Player, domain.RSVP) (domain.Player, domain.RSVP, error)
 	CreateEvent(context.Context, domain.Event) (domain.Event, error)
 	GetEvent(context.Context, string) (domain.Event, error)
 	UpdateEvent(context.Context, domain.Event) (domain.Event, error)
@@ -174,6 +176,47 @@ func (s *Service) SetRSVP(ctx context.Context, actor domain.Account, actorPlayer
 	return out, err
 }
 
+func (s *Service) CreateParticipant(ctx context.Context, actor domain.Account, eventID, displayName string, ratings domain.Ratings, status domain.RSVPStatus) (domain.Player, domain.RSVP, error) {
+	if !actor.IsAdmin() {
+		return domain.Player{}, domain.RSVP{}, domain.ErrForbidden
+	}
+	displayName = strings.TrimSpace(displayName)
+	if displayName == "" {
+		return domain.Player{}, domain.RSVP{}, fmt.Errorf("%w: display name is required", domain.ErrInvalid)
+	}
+	if err := ratings.Validate(); err != nil {
+		return domain.Player{}, domain.RSVP{}, err
+	}
+	if _, err := s.Store.GetEvent(ctx, eventID); err != nil {
+		return domain.Player{}, domain.RSVP{}, err
+	}
+	now := s.Now()
+	player := domain.Player{
+		ID:          NewID(),
+		DisplayName: displayName,
+		Ratings:     ratings,
+		CreatedAt:   now,
+		UpdatedAt:   now,
+	}
+	rsvp := domain.RSVP{
+		EventID:        eventID,
+		PlayerID:       player.ID,
+		ActorAccountID: actor.ID,
+		Status:         status,
+		Source:         domain.SourceAdmin,
+		UpdatedAt:      now,
+	}
+	if err := rsvp.Validate(); err != nil {
+		return domain.Player{}, domain.RSVP{}, err
+	}
+	player, rsvp, err := s.Store.CreateParticipant(ctx, player, rsvp)
+	if err == nil {
+		_ = s.Store.AppendAudit(ctx, actor.ID, "participant.created", eventID, map[string]any{"player": player, "rsvp": rsvp})
+		s.Bus.Publish("event:"+eventID, rsvp)
+	}
+	return player, rsvp, err
+}
+
 func (s *Service) Balance(ctx context.Context, actor domain.Account, eventID string) ([]domain.BalanceCandidate, error) {
 	if !actor.IsAdmin() {
 		return nil, domain.ErrForbidden