refactor(channelserver): extract Event, Achievement, Shop, and Cafe repositories

Move 22 raw SQL queries from 4 handler files into dedicated repository
structs, continuing the repository extraction pattern. Achievement
insert uses ON CONFLICT DO NOTHING to eliminate check-then-insert race,
and IncrementScore validates the column index to prevent SQL injection.

server/channelserver/sys_channel_server.go

@@ -58,6 +58,10 @@ type Server struct {
 	stampRepo      *StampRepository
 	distRepo       *DistributionRepository
 	sessionRepo    *SessionRepository
+	eventRepo      *EventRepository
+	achievementRepo *AchievementRepository
+	shopRepo       *ShopRepository
+	cafeRepo       *CafeRepository
 	erupeConfig    *_config.Config
 	acceptConns    chan net.Conn
 	deleteConns    chan net.Conn
@@ -140,6 +144,10 @@ func NewServer(config *Config) *Server {
 	s.stampRepo = NewStampRepository(config.DB)
 	s.distRepo = NewDistributionRepository(config.DB)
 	s.sessionRepo = NewSessionRepository(config.DB)
+	s.eventRepo = NewEventRepository(config.DB)
+	s.achievementRepo = NewAchievementRepository(config.DB)
+	s.shopRepo = NewShopRepository(config.DB)
+	s.cafeRepo = NewCafeRepository(config.DB)
 
 	// Mezeporta
 	s.stages["sl1Ns200p0a0u0"] = NewStage("sl1Ns200p0a0u0")