refactor(channelserver): extract GuildRepository for guild table access

Per anti-patterns.md item #9, guild-related SQL was scattered across
~15 handler files with no repository abstraction. Following the same
pattern established by CharacterRepository, this centralizes all
guilds, guild_characters, and guild_applications table access into a
single GuildRepository (~30 methods).

guild_model.go and handlers_guild_member.go are trimmed to types and
pure business logic only. All handler files (guild_*, festa, mail,
house, mercenary, rengoku) now call s.server.guildRepo methods
instead of direct DB queries or methods on domain objects.

server/channelserver/sys_channel_server.go

@@ -46,6 +46,7 @@ type Server struct {
 	logger         *zap.Logger
 	db             *sqlx.DB
 	charRepo       *CharacterRepository
+	guildRepo      *GuildRepository
 	erupeConfig    *_config.Config
 	acceptConns    chan net.Conn
 	deleteConns    chan net.Conn
@@ -117,6 +118,7 @@ func NewServer(config *Config) *Server {
 	}
 
 	s.charRepo = NewCharacterRepository(config.DB)
+	s.guildRepo = NewGuildRepository(config.DB)
 
 	// Mezeporta
 	s.stages["sl1Ns200p0a0u0"] = NewStage("sl1Ns200p0a0u0")