refactor(channelserver): replace magic numbers with named protocol constants

Extract numeric literals into named constants across quest handling,
save data parsing, rengoku skill layout, diva event timing, guild info,
achievement trophies, RP accrual rates, and semaphore IDs. Adds
constants_quest.go for quest-related constants shared across functions.

Pure rename/extract with zero behavior change.

server/channelserver/handlers_guild_info.go

@@ -12,6 +12,12 @@ import (
 	"github.com/jmoiron/sqlx"
 )
 
+// Guild sentinel and cost constants
+const (
+	guildNotJoinedSentinel = uint32(0xFFFFFFFF)
+	guildRoomMaxRP         = uint32(55000)
+)
+
 func handleMsgMhfInfoGuild(s *Session, p mhfpacket.MHFPacket) {
 	pkt := p.(*mhfpacket.MsgMhfInfoGuild)
 
@@ -32,7 +38,7 @@ func handleMsgMhfInfoGuild(s *Session, p mhfpacket.MHFPacket) {
 		guildLeaderName := stringsupport.UTF8ToSJIS(guild.LeaderName)
 
 		characterGuildData, err := GetCharacterGuildData(s, s.charID)
-		characterJoinedAt := uint32(0xFFFFFFFF)
+		characterJoinedAt := guildNotJoinedSentinel
 
 		if characterGuildData != nil && characterGuildData.JoinedAt != nil {
 			characterJoinedAt = uint32(characterGuildData.JoinedAt.Unix())
@@ -123,7 +129,7 @@ func handleMsgMhfInfoGuild(s *Session, p mhfpacket.MHFPacket) {
 		}
 		bf.WriteUint8(limit)
 
-		bf.WriteUint32(55000)
+		bf.WriteUint32(guildRoomMaxRP)
 		bf.WriteUint32(uint32(guild.RoomExpiry.Unix()))
 		bf.WriteUint16(guild.RoomRP)
 		bf.WriteUint16(0) // Ignored