refactor(mhfpacket): rename 15 Unk fields with identified meanings

Replace unknown field names with descriptive names based on handler
logic analysis, switch dispatch patterns, DB query context, and
inline comments:

- ObjectHandleID, IsQuest, ItemIDCount, MaxCount, TokenLength,
  FormatVersion, LogoutType (high confidence from comments/constants)
- QueryType, DataType, MissionIndex, CheckOnly, RequestType,
  ExchangeType, TournamentID (confirmed by handler switch/if usage)

Also fix MsgSysLogout.Build calling ReadUint8 instead of WriteUint8.

network/mhfpacket/msg_sys_logout.go

@@ -8,7 +8,7 @@ import (
 
 // MsgSysLogout represents the MSG_SYS_LOGOUT
 type MsgSysLogout struct {
-	Unk0 uint8 // Hardcoded 1 in binary
+	LogoutType uint8 // Hardcoded 1 in binary
 }
 
 // Opcode returns the ID associated with this packet type.
@@ -18,12 +18,12 @@ func (m *MsgSysLogout) Opcode() network.PacketID {
 
 // Parse parses the packet from binary
 func (m *MsgSysLogout) Parse(bf *byteframe.ByteFrame, ctx *clientctx.ClientContext) error {
-	m.Unk0 = bf.ReadUint8()
+	m.LogoutType = bf.ReadUint8()
 	return nil
 }
 
 // Build builds a binary packet from the current data.
 func (m *MsgSysLogout) Build(bf *byteframe.ByteFrame, ctx *clientctx.ClientContext) error {
-	m.Unk0 = bf.ReadUint8()
+	bf.WriteUint8(m.LogoutType)
 	return nil
 }