fix: re-enable CI lint job and fix ~65 lint errors (partial)

Re-enable the golangci-lint job in CI (disabled Oct 2025), update to
Go 1.25 and golangci-lint-action v7. Fix errcheck, gosimple S1009,
staticcheck SA4031 and SA2001 errors across 54 files. Remaining ~39
lint errors will be addressed in follow-up commits.

server/channelserver/handlers_tower.go

@@ -324,7 +324,7 @@ func handleMsgMhfGetTenrouirai(s *Session, p mhfpacket.MHFPacket) {
 			defer rows.Close()
 			for rows.Next() {
 				temp := TenrouiraiCharScore{}
-				rows.Scan(&temp.Name, &temp.Score)
+				_ = rows.Scan(&temp.Name, &temp.Score)
 				tenrouirai.CharScore = append(tenrouirai.CharScore, temp)
 			}
 		}