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/test_helpers_test.go

@@ -48,6 +48,9 @@ func createMockServer() *Server {
 			state:    make([]uint32, 30),
 			support:  make([]uint32, 30),
 		},
+		// divaRepo default prevents nil-deref in diva handler tests that don't
+		// need specific repo behaviour. Tests that need controlled data override it.
+		divaRepo: &mockDivaRepo{},
 	}
 	s.i18n = getLangStrings(s)
 	s.Registry = NewLocalChannelRegistry([]*Server{s})