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/conn.go

@@ -0,0 +1,52 @@
+package conn
+
+import (
+	"fmt"
+	"net"
+)
+
+// MHFConn wraps a CryptConn and provides convenience methods for MHF connections.
+type MHFConn struct {
+	*CryptConn
+	RawConn net.Conn
+}
+
+// DialWithInit connects to addr and sends the 8 NULL byte initialization
+// required by sign and entrance servers.
+func DialWithInit(addr string) (*MHFConn, error) {
+	conn, err := net.Dial("tcp", addr)
+	if err != nil {
+		return nil, fmt.Errorf("dial %s: %w", addr, err)
+	}
+
+	// Sign and entrance servers expect 8 NULL bytes to initialize the connection.
+	_, err = conn.Write(make([]byte, 8))
+	if err != nil {
+		conn.Close()
+		return nil, fmt.Errorf("write init bytes to %s: %w", addr, err)
+	}
+
+	return &MHFConn{
+		CryptConn: NewCryptConn(conn),
+		RawConn:   conn,
+	}, nil
+}
+
+// DialDirect connects to addr without sending initialization bytes.
+// Used for channel server connections.
+func DialDirect(addr string) (*MHFConn, error) {
+	conn, err := net.Dial("tcp", addr)
+	if err != nil {
+		return nil, fmt.Errorf("dial %s: %w", addr, err)
+	}
+
+	return &MHFConn{
+		CryptConn: NewCryptConn(conn),
+		RawConn:   conn,
+	}, nil
+}
+
+// Close closes the underlying connection.
+func (c *MHFConn) Close() error {
+	return c.RawConn.Close()
+}