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)

server/channelserver/sys_session.go

@@ -72,6 +72,10 @@ type Session struct {
 	// Contains the mail list that maps accumulated indexes to mail IDs
 	mailList []int
 
+	// currentBeadIndex is the bead slot selected by the player via MsgMhfSetKiju.
+	// A value of -1 means no bead is currently assigned this session.
+	currentBeadIndex int
+
 	Name           string
 	closed         atomic.Bool
 	ackStart       map[uint32]time.Time
@@ -86,20 +90,21 @@ func NewSession(server *Server, conn net.Conn) *Session {
 	cryptConn, captureConn, captureCleanup := startCapture(server, cryptConn, conn.RemoteAddr(), pcap.ServerTypeChannel)
 
 	s := &Session{
-		logger:         server.logger.Named(conn.RemoteAddr().String()),
-		server:         server,
-		rawConn:        conn,
-		cryptConn:      cryptConn,
-		sendPackets:    make(chan packet, 20),
-		clientContext:  &clientctx.ClientContext{RealClientMode: server.erupeConfig.RealClientMode},
-		lastPacket:     time.Now(),
-		objectID:       server.getObjectId(),
-		sessionStart:   TimeAdjusted().Unix(),
-		stageMoveStack: stringstack.New(),
-		ackStart:       make(map[uint32]time.Time),
-		semaphoreID:    make([]uint16, 2),
-		captureConn:    captureConn,
-		captureCleanup: captureCleanup,
+		logger:           server.logger.Named(conn.RemoteAddr().String()),
+		server:           server,
+		rawConn:          conn,
+		cryptConn:        cryptConn,
+		sendPackets:      make(chan packet, 20),
+		clientContext:    &clientctx.ClientContext{RealClientMode: server.erupeConfig.RealClientMode},
+		lastPacket:       time.Now(),
+		objectID:         server.getObjectId(),
+		sessionStart:     TimeAdjusted().Unix(),
+		stageMoveStack:   stringstack.New(),
+		ackStart:         make(map[uint32]time.Time),
+		semaphoreID:      make([]uint16, 2),
+		captureConn:      captureConn,
+		captureCleanup:   captureCleanup,
+		currentBeadIndex: -1,
 	}
 	return s
 }