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_session.go

@@ -500,12 +500,12 @@ func handleMsgMhfTransitMessage(s *Session, p mhfpacket.MHFPacket) {
 	case 1, 2, 3: // usersearchidx, usersearchname, lobbysearchname
 		// Snapshot matching sessions under lock, then build response outside locks.
 		type sessionResult struct {
-			charID    uint32
-			name      []byte
-			stageID   []byte
-			ip        net.IP
-			port      uint16
-			userBin3  []byte
+			charID   uint32
+			name     []byte
+			stageID  []byte
+			ip       net.IP
+			port     uint16
+			userBin3 []byte
 		}
 		var results []sessionResult
 
@@ -656,15 +656,15 @@ func handleMsgMhfTransitMessage(s *Session, p mhfpacket.MHFPacket) {
 		}
 		// Snapshot matching stages under lock, then build response outside locks.
 		type stageResult struct {
-			ip           net.IP
-			port         uint16
-			clientCount  int
-			reserved     int
-			maxPlayers   uint16
-			stageID      string
-			stageData    []int16
-			rawBinData0  []byte
-			rawBinData1  []byte
+			ip          net.IP
+			port        uint16
+			clientCount int
+			reserved    int
+			maxPlayers  uint16
+			stageID     string
+			stageData   []int16
+			rawBinData0 []byte
+			rawBinData1 []byte
 		}
 		var stageResults []stageResult