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/constants_time.go

@@ -0,0 +1,7 @@
+package channelserver
+
+// Shared time duration constants (seconds)
+const (
+	secsPerDay  = 86400  // 24 hours
+	secsPerWeek = 604800 // 7 days
+)