feat(achievement): add rank-up notifications (#165)

RE'd putDisplayed_achievement from ZZ client DLL via Ghidra: the packet
sends opcode + 1 zero byte with no achievement ID, acting as a blanket
"I saw everything" signal.

Server changes:
- Track per-character last-displayed levels in new displayed_levels
  column (migration 0008)
- GetAchievement compares current vs displayed levels per entry
- DisplayedAchievement snapshots current levels to clear notifications
- Repo, service, mock, and 3 new service tests

Protbot changes:
- New --action achievement: fetches achievements, shows rank-up markers,
  sends DISPLAYED_ACHIEVEMENT, re-fetches to verify notifications clear
- Packet builders for GET/ADD/DISPLAYED_ACHIEVEMENT

cmd/protbot/scenario/achievement.go

@@ -0,0 +1,93 @@
+package scenario
+
+import (
+	"fmt"
+	"time"
+
+	"erupe-ce/cmd/protbot/protocol"
+	"erupe-ce/common/byteframe"
+)
+
+// AchievementEntry holds parsed achievement data from the server response.
+type AchievementEntry struct {
+	ID       uint8
+	Level    uint8
+	Next     uint16
+	Required uint32
+	Notify   bool
+	Trophy   uint8
+	Progress uint32
+}
+
+// AchievementResult holds the full parsed GET_ACHIEVEMENT response.
+type AchievementResult struct {
+	Points  uint32
+	Entries []AchievementEntry
+}
+
+// GetAchievements sends MSG_MHF_GET_ACHIEVEMENT and returns the parsed response.
+func GetAchievements(ch *protocol.ChannelConn, charID uint32) (*AchievementResult, error) {
+	ack := ch.NextAckHandle()
+	pkt := protocol.BuildGetAchievementPacket(ack, charID)
+	fmt.Printf("[achievement] Sending GET_ACHIEVEMENT (charID=%d, ackHandle=%d)...\n", charID, ack)
+	if err := ch.SendPacket(pkt); err != nil {
+		return nil, fmt.Errorf("get achievement send: %w", err)
+	}
+
+	resp, err := ch.WaitForAck(ack, 10*time.Second)
+	if err != nil {
+		return nil, fmt.Errorf("get achievement ack: %w", err)
+	}
+	if resp.ErrorCode != 0 {
+		return nil, fmt.Errorf("get achievement failed: error code %d", resp.ErrorCode)
+	}
+	fmt.Printf("[achievement] ACK received (%d bytes)\n", len(resp.Data))
+
+	return parseAchievementResponse(resp.Data)
+}
+
+// IncrementAchievement sends MSG_MHF_ADD_ACHIEVEMENT (fire-and-forget, no ACK).
+func IncrementAchievement(ch *protocol.ChannelConn, achievementID uint8) error {
+	pkt := protocol.BuildAddAchievementPacket(achievementID)
+	fmt.Printf("[achievement] Sending ADD_ACHIEVEMENT (id=%d)...\n", achievementID)
+	return ch.SendPacket(pkt)
+}
+
+// DisplayedAchievement sends MSG_MHF_DISPLAYED_ACHIEVEMENT to tell the server
+// the client has seen all rank-up notifications (fire-and-forget, no ACK).
+func DisplayedAchievement(ch *protocol.ChannelConn) error {
+	pkt := protocol.BuildDisplayedAchievementPacket()
+	fmt.Printf("[achievement] Sending DISPLAYED_ACHIEVEMENT...\n")
+	return ch.SendPacket(pkt)
+}
+
+func parseAchievementResponse(data []byte) (*AchievementResult, error) {
+	if len(data) < 20 {
+		return nil, fmt.Errorf("achievement response too short: %d bytes", len(data))
+	}
+
+	bf := byteframe.NewByteFrameFromBytes(data)
+	result := &AchievementResult{}
+
+	// Header: 4x uint32 points (all same value), 3 bytes unk, 1 byte count
+	result.Points = bf.ReadUint32()
+	bf.ReadUint32() // Points repeated
+	bf.ReadUint32() // Points repeated
+	bf.ReadUint32() // Points repeated
+	bf.ReadBytes(3) // Unk (0x02, 0x00, 0x00)
+	count := bf.ReadUint8()
+
+	for i := uint8(0); i < count; i++ {
+		entry := AchievementEntry{}
+		entry.ID = bf.ReadUint8()
+		entry.Level = bf.ReadUint8()
+		entry.Next = bf.ReadUint16()
+		entry.Required = bf.ReadUint32()
+		entry.Notify = bf.ReadBool()
+		entry.Trophy = bf.ReadUint8()
+		bf.ReadUint16() // Unk
+		entry.Progress = bf.ReadUint32()
+		result.Entries = append(result.Entries, entry)
+	}
+	return result, nil
+}