refactor(channelserver): add numeric column helpers and extract protocol constants

Add readCharacterInt/adjustCharacterInt helpers for single-column
integer operations on the characters table. Eliminates fmt.Sprintf
SQL construction in handlers_misc.go and replaces inline queries
across cafe, kouryou, and mercenary handlers.

Second round of protocol constant extraction: adds constants_time.go
(secsPerDay, secsPerWeek), constants_raviente.go (register IDs,
semaphore constants), and named constants across 14 handler files
replacing raw hex/numeric literals. Updates anti-patterns doc to
mark #4 (magic numbers) as substantially fixed.

server/channelserver/handlers_diva.go

@@ -15,7 +15,7 @@ import (
 const (
 	divaPhaseDuration = 601200  // 6d 23h = first song phase
 	divaInterlude     = 3900    // 65 min = gap between phases
-	divaWeekDuration  = 604800  // 7 days = subsequent phase length
+	divaWeekDuration  = secsPerWeek // 7 days = subsequent phase length
 	divaTotalLifespan = 2977200 // ~34.5 days = full event window
 )
 
@@ -76,7 +76,8 @@ func handleMsgMhfGetUdSchedule(s *Session, p mhfpacket.MHFPacket) {
 	pkt := p.(*mhfpacket.MsgMhfGetUdSchedule)
 	bf := byteframe.NewByteFrame()
 
-	id, start := uint32(0xCAFEBEEF), uint32(0)
+	const divaIDSentinel = uint32(0xCAFEBEEF)
+	id, start := divaIDSentinel, uint32(0)
 	rows, err := s.server.db.Queryx("SELECT id, (EXTRACT(epoch FROM start_time)::int) as start_time FROM events WHERE event_type='diva'")
 	if err != nil {
 		s.logger.Error("Failed to query diva schedule", zap.Error(err))