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/scenario/login.go

@@ -0,0 +1,82 @@
+// Package scenario provides high-level MHF protocol flows.
+package scenario
+
+import (
+	"fmt"
+	"time"
+
+	"erupe-ce/cmd/protbot/protocol"
+)
+
+// LoginResult holds the outcome of a full login flow.
+type LoginResult struct {
+	Sign    *protocol.SignResult
+	Servers []protocol.ServerEntry
+	Channel *protocol.ChannelConn
+}
+
+// Login performs the full sign → entrance → channel login flow.
+func Login(signAddr, username, password string) (*LoginResult, error) {
+	// Step 1: Sign server authentication.
+	fmt.Printf("[sign] Connecting to %s...\n", signAddr)
+	sign, err := protocol.DoSign(signAddr, username, password)
+	if err != nil {
+		return nil, fmt.Errorf("sign: %w", err)
+	}
+	fmt.Printf("[sign] OK — tokenID=%d, %d character(s), entrance=%s\n",
+		sign.TokenID, len(sign.CharIDs), sign.EntranceAddr)
+
+	if len(sign.CharIDs) == 0 {
+		return nil, fmt.Errorf("no characters on account")
+	}
+
+	// Step 2: Entrance server — get server/channel list.
+	fmt.Printf("[entrance] Connecting to %s...\n", sign.EntranceAddr)
+	servers, err := protocol.DoEntrance(sign.EntranceAddr)
+	if err != nil {
+		return nil, fmt.Errorf("entrance: %w", err)
+	}
+	if len(servers) == 0 {
+		return nil, fmt.Errorf("no channels available")
+	}
+	for i, s := range servers {
+		fmt.Printf("[entrance]   [%d] %s — %s:%d\n", i, s.Name, s.IP, s.Port)
+	}
+
+	// Step 3: Connect to the first channel server.
+	first := servers[0]
+	channelAddr := fmt.Sprintf("%s:%d", first.IP, first.Port)
+	fmt.Printf("[channel] Connecting to %s...\n", channelAddr)
+	ch, err := protocol.ConnectChannel(channelAddr)
+	if err != nil {
+		return nil, fmt.Errorf("channel connect: %w", err)
+	}
+
+	// Step 4: Send MSG_SYS_LOGIN.
+	charID := sign.CharIDs[0]
+	ack := ch.NextAckHandle()
+	loginPkt := protocol.BuildLoginPacket(ack, charID, sign.TokenID, sign.TokenString)
+	fmt.Printf("[channel] Sending MSG_SYS_LOGIN (charID=%d, ackHandle=%d)...\n", charID, ack)
+	if err := ch.SendPacket(loginPkt); err != nil {
+		ch.Close()
+		return nil, fmt.Errorf("channel send login: %w", err)
+	}
+
+	resp, err := ch.WaitForAck(ack, 10*time.Second)
+	if err != nil {
+		ch.Close()
+		return nil, fmt.Errorf("channel login ack: %w", err)
+	}
+	if resp.ErrorCode != 0 {
+		ch.Close()
+		return nil, fmt.Errorf("channel login failed: error code %d", resp.ErrorCode)
+	}
+	fmt.Printf("[channel] Login ACK received (error=%d, %d bytes data)\n",
+		resp.ErrorCode, len(resp.Data))
+
+	return &LoginResult{
+		Sign:    sign,
+		Servers: servers,
+		Channel: ch,
+	}, nil
+}