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_helpers.go

@@ -96,6 +96,22 @@ func saveCharacterData(s *Session, ackHandle uint32, column string, data []byte,
 	doAckSimpleSucceed(s, ackHandle, make([]byte, 4))
 }
 
+// readCharacterInt reads a single integer column from the characters table.
+// Returns 0 for NULL columns via COALESCE.
+func readCharacterInt(s *Session, column string) (int, error) {
+	var value int
+	err := s.server.db.QueryRow("SELECT COALESCE("+column+", 0) FROM characters WHERE id=$1", s.charID).Scan(&value)
+	return value, err
+}
+
+// adjustCharacterInt atomically adds delta to an integer column and returns the new value.
+// Handles NULL columns via COALESCE (NULL + delta = delta).
+func adjustCharacterInt(s *Session, column string, delta int) (int, error) {
+	var value int
+	err := s.server.db.QueryRow("UPDATE characters SET "+column+"=COALESCE("+column+", 0)+$1 WHERE id=$2 RETURNING "+column, delta, s.charID).Scan(&value)
+	return value, err
+}
+
 func updateRights(s *Session) {
 	rightsInt := uint32(2)
 	_ = s.server.db.QueryRow("SELECT rights FROM users WHERE id=$1", s.userID).Scan(&rightsInt)