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/protocol/opcodes.go

@@ -19,5 +19,8 @@ const (
 	MSG_SYS_RIGHTS_RELOAD    uint16 = 0x005D
 	MSG_MHF_LOADDATA         uint16 = 0x0061
 	MSG_MHF_ENUMERATE_QUEST  uint16 = 0x009F
-	MSG_MHF_GET_WEEKLY_SCHED uint16 = 0x00E1
+	MSG_MHF_GET_ACHIEVEMENT       uint16 = 0x00D4
+	MSG_MHF_ADD_ACHIEVEMENT       uint16 = 0x00D6
+	MSG_MHF_DISPLAYED_ACHIEVEMENT uint16 = 0x00D8
+	MSG_MHF_GET_WEEKLY_SCHED      uint16 = 0x00E1
 )

cmd/protbot/protocol/packets.go

@@ -215,6 +215,56 @@ func BuildEnumerateQuestPacket(ackHandle uint32, world uint8, counter, offset ui
 	return bf.Data()
 }
 
+// BuildGetAchievementPacket builds a MSG_MHF_GET_ACHIEVEMENT packet.
+// Layout mirrors Erupe's MsgMhfGetAchievement.Parse:
+//
+//	uint16 opcode
+//	uint32 ackHandle
+//	uint32 charID
+//	uint32 zeroed
+//	0x00 0x10 terminator
+func BuildGetAchievementPacket(ackHandle, charID uint32) []byte {
+	bf := byteframe.NewByteFrame()
+	bf.WriteUint16(MSG_MHF_GET_ACHIEVEMENT)
+	bf.WriteUint32(ackHandle)
+	bf.WriteUint32(charID)
+	bf.WriteUint32(0) // Zeroed
+	bf.WriteBytes([]byte{0x00, 0x10})
+	return bf.Data()
+}
+
+// BuildAddAchievementPacket builds a MSG_MHF_ADD_ACHIEVEMENT packet (fire-and-forget, no ACK).
+// Layout mirrors Erupe's MsgMhfAddAchievement.Parse:
+//
+//	uint16 opcode
+//	uint8  achievementID
+//	uint16 unk1
+//	uint16 unk2
+//	0x00 0x10 terminator
+func BuildAddAchievementPacket(achievementID uint8) []byte {
+	bf := byteframe.NewByteFrame()
+	bf.WriteUint16(MSG_MHF_ADD_ACHIEVEMENT)
+	bf.WriteUint8(achievementID)
+	bf.WriteUint16(0) // Unk1
+	bf.WriteUint16(0) // Unk2
+	bf.WriteBytes([]byte{0x00, 0x10})
+	return bf.Data()
+}
+
+// BuildDisplayedAchievementPacket builds a MSG_MHF_DISPLAYED_ACHIEVEMENT packet (fire-and-forget).
+// Layout mirrors Erupe's MsgMhfDisplayedAchievement.Parse:
+//
+//	uint16 opcode
+//	uint8  zeroed
+//	0x00 0x10 terminator
+func BuildDisplayedAchievementPacket() []byte {
+	bf := byteframe.NewByteFrame()
+	bf.WriteUint16(MSG_MHF_DISPLAYED_ACHIEVEMENT)
+	bf.WriteUint8(0) // Zeroed
+	bf.WriteBytes([]byte{0x00, 0x10})
+	return bf.Data()
+}
+
 // BuildGetWeeklySchedulePacket builds a MSG_MHF_GET_WEEKLY_SCHEDULE packet.
 //
 //	uint16 opcode