feat(protbot): add headless MHF protocol bot as cmd/protbot

Copy MHBridge into the Erupe module as cmd/protbot/ so it can be
built, tested, and maintained alongside the server. The bot
implements the full sign → entrance → channel login flow and
supports lobby entry, chat, session setup, and quest enumeration.

The conn/ package keeps its own Blowfish crypto primitives to avoid
importing erupe-ce/config (which requires a config file at init).

cmd/protbot/conn/crypt_packet.go

@@ -0,0 +1,78 @@
+// Package conn provides MHF encrypted connection primitives.
+//
+// This is adapted from Erupe's network/crypt_packet.go to avoid importing
+// erupe-ce/config (whose init() calls os.Exit without a config file).
+package conn
+
+import (
+	"bytes"
+	"encoding/binary"
+)
+
+const CryptPacketHeaderLength = 14
+
+// CryptPacketHeader represents the parsed information of an encrypted packet header.
+type CryptPacketHeader struct {
+	Pf0                     byte
+	KeyRotDelta             byte
+	PacketNum               uint16
+	DataSize                uint16
+	PrevPacketCombinedCheck uint16
+	Check0                  uint16
+	Check1                  uint16
+	Check2                  uint16
+}
+
+// NewCryptPacketHeader parses raw bytes into a CryptPacketHeader.
+func NewCryptPacketHeader(data []byte) (*CryptPacketHeader, error) {
+	var c CryptPacketHeader
+	r := bytes.NewReader(data)
+
+	if err := binary.Read(r, binary.BigEndian, &c.Pf0); err != nil {
+		return nil, err
+	}
+	if err := binary.Read(r, binary.BigEndian, &c.KeyRotDelta); err != nil {
+		return nil, err
+	}
+	if err := binary.Read(r, binary.BigEndian, &c.PacketNum); err != nil {
+		return nil, err
+	}
+	if err := binary.Read(r, binary.BigEndian, &c.DataSize); err != nil {
+		return nil, err
+	}
+	if err := binary.Read(r, binary.BigEndian, &c.PrevPacketCombinedCheck); err != nil {
+		return nil, err
+	}
+	if err := binary.Read(r, binary.BigEndian, &c.Check0); err != nil {
+		return nil, err
+	}
+	if err := binary.Read(r, binary.BigEndian, &c.Check1); err != nil {
+		return nil, err
+	}
+	if err := binary.Read(r, binary.BigEndian, &c.Check2); err != nil {
+		return nil, err
+	}
+
+	return &c, nil
+}
+
+// Encode encodes the CryptPacketHeader into raw bytes.
+func (c *CryptPacketHeader) Encode() ([]byte, error) {
+	buf := bytes.NewBuffer([]byte{})
+	data := []interface{}{
+		c.Pf0,
+		c.KeyRotDelta,
+		c.PacketNum,
+		c.DataSize,
+		c.PrevPacketCombinedCheck,
+		c.Check0,
+		c.Check1,
+		c.Check2,
+	}
+	for _, v := range data {
+		if err := binary.Write(buf, binary.BigEndian, v); err != nil {
+			return nil, err
+		}
+	}
+	return buf.Bytes(), nil
+}