test: increase code coverage from 45.1% to 48.3%

Add unit tests across multiple packages:
- byteframe: SetBE/SetLE byte order switching
- config: Mode.String() for all safe version ranges
- mhfpacket: 28 Parse methods, 5 Build methods, empty packet builds,
  variable-length packets, NOT IMPLEMENTED error paths, UpdateWarehouse
- network: PacketID.String() for known IDs, out-of-range, and all valid
- channelserver: handleMsgMhfGetPaperData (6 switch cases), grpToGR
  (11 input values), gacha handlers, TimeGameAbsolute, equipSkinHistSize
  (4 config branches), guild mission handlers, dumpSaveData disabled path
- entranceserver: makeHeader with various inputs

common/byteframe/byteframe_setbe_test.go

@@ -0,0 +1,58 @@
+package byteframe
+
+import (
+	"encoding/binary"
+	"io"
+	"testing"
+)
+
+func TestByteFrame_SetBE(t *testing.T) {
+	bf := NewByteFrame()
+	// Default is already BigEndian, switch to LE first
+	bf.SetLE()
+	if bf.byteOrder != binary.LittleEndian {
+		t.Error("SetLE() should set LittleEndian")
+	}
+
+	// Now test SetBE
+	bf.SetBE()
+	if bf.byteOrder != binary.BigEndian {
+		t.Error("SetBE() should set BigEndian")
+	}
+
+	// Verify write/read works correctly in BE mode after switching
+	bf.WriteUint16(0x1234)
+	bf.Seek(0, io.SeekStart)
+	got := bf.ReadUint16()
+	if got != 0x1234 {
+		t.Errorf("ReadUint16() = 0x%04X, want 0x1234", got)
+	}
+
+	// Verify raw bytes are in big endian order
+	bf2 := NewByteFrame()
+	bf2.SetLE()
+	bf2.SetBE()
+	bf2.WriteUint32(0xDEADBEEF)
+	data := bf2.Data()
+	if data[0] != 0xDE || data[1] != 0xAD || data[2] != 0xBE || data[3] != 0xEF {
+		t.Errorf("SetBE bytes: got %X, want DEADBEEF", data)
+	}
+}
+
+func TestByteFrame_LEReadWrite(t *testing.T) {
+	bf := NewByteFrame()
+	bf.SetLE()
+
+	bf.WriteUint32(0x12345678)
+	data := bf.Data()
+	// In LE, LSB first
+	if data[0] != 0x78 || data[1] != 0x56 || data[2] != 0x34 || data[3] != 0x12 {
+		t.Errorf("LE WriteUint32 bytes: got %X, want 78563412", data)
+	}
+
+	bf.Seek(0, io.SeekStart)
+	got := bf.ReadUint32()
+	if got != 0x12345678 {
+		t.Errorf("LE ReadUint32() = 0x%08X, want 0x12345678", got)
+	}
+}