feat(diva): implement Diva Defense (UD) system

Add full Diva Defense / United Defense system: schema, repo layer,
i18n bead names, and RE-verified packet handler implementations.

Schema (0011_diva.sql): diva_beads, diva_beads_assignment,
diva_beads_points, diva_prizes tables; interception_maps/points
columns on guilds and guild_characters.

Seed (DivaDefaults.sql): 26 prize milestones for personal and
guild reward tracks (item_type=26 diva coins).

Repo (DivaRepo): 11 new methods covering bead assignment, point
accumulation, interception point tracking, prize queries, and
cleanup. Mocks wired in test_helpers_test.go.

i18n: Bead struct with EN/JP names for all 18 bead types (IDs
1–25). Session tracks currentBeadIndex (-1 = none assigned).

Packet handlers corrected against mhfo-hd.dll RE findings:
- GetKijuInfo: u8 count, 512-byte desc, color_id+bead_type per entry
- SetKiju: 1-byte ACK; persists bead assignment to DB
- GetUdMyPoint: 8×18-byte entries, no count prefix
- GetUdTotalPointInfo: u8 error + u64[64] + u8[64] + u64 (~585 B)
- GetUdSelectedColorInfo: u8 error + u8[8] = 9 bytes
- GetUdDailyPresentList: correct u16 count format (was wrong hex)
- GetUdNormaPresentList: correct u16 count format (was wrong hex)
- GetUdRankingRewardList: correct u16 count with u32 item_id/qty
- GetRewardSong: 22-byte layout with 0xFFFFFFFF prayer_end sentinel
- AddRewardSongCount: parse implemented (was NOT IMPLEMENTED stub)

network/mhfpacket/msg_mhf_add_reward_song_count.go

@@ -1,27 +1,53 @@
 package mhfpacket
 
 import (
-	"errors"
-
 	"erupe-ce/common/byteframe"
 	"erupe-ce/network"
 	"erupe-ce/network/clientctx"
 )
 
-// MsgMhfAddRewardSongCount represents the MSG_MHF_ADD_REWARD_SONG_COUNT
-type MsgMhfAddRewardSongCount struct{}
+// MsgMhfAddRewardSongCount represents the MSG_MHF_ADD_REWARD_SONG_COUNT packet.
+// Request layout:
+//
+//	u32 ack_handle
+//	u32 prayer_id
+//	u16 array_size_bytes  (= count × 2)
+//	u8  count
+//	u16[count] entries
+type MsgMhfAddRewardSongCount struct {
+	AckHandle      uint32
+	PrayerID       uint32
+	ArraySizeBytes uint16
+	Count          uint8
+	Entries        []uint16
+}
 
 // Opcode returns the ID associated with this packet type.
 func (m *MsgMhfAddRewardSongCount) Opcode() network.PacketID {
 	return network.MSG_MHF_ADD_REWARD_SONG_COUNT
 }
 
-// Parse parses the packet from binary
+// Parse parses the packet from binary.
 func (m *MsgMhfAddRewardSongCount) Parse(bf *byteframe.ByteFrame, ctx *clientctx.ClientContext) error {
-	return errors.New("NOT IMPLEMENTED")
+	m.AckHandle = bf.ReadUint32()
+	m.PrayerID = bf.ReadUint32()
+	m.ArraySizeBytes = bf.ReadUint16()
+	m.Count = bf.ReadUint8()
+	m.Entries = make([]uint16, m.Count)
+	for i := range m.Entries {
+		m.Entries[i] = bf.ReadUint16()
+	}
+	return bf.Err()
 }
 
 // Build builds a binary packet from the current data.
 func (m *MsgMhfAddRewardSongCount) Build(bf *byteframe.ByteFrame, ctx *clientctx.ClientContext) error {
-	return errors.New("NOT IMPLEMENTED")
+	bf.WriteUint32(m.AckHandle)
+	bf.WriteUint32(m.PrayerID)
+	bf.WriteUint16(uint16(len(m.Entries) * 2))
+	bf.WriteUint8(uint8(len(m.Entries)))
+	for _, e := range m.Entries {
+		bf.WriteUint16(e)
+	}
+	return nil
 }