Fix emend. author bug in get_author_year() and update ref documentation

Strip emend. and everything after it so the ref column retains the
combination authority, not the emendation author. Update data.R and
mo_property.R docs to describe the correct semantics of the ref field.

https://claude.ai/code/session_01VH4Ju4Xq9aW1AHuoVbjGEo

data-raw/_reproduction_scripts/reproduction_of_microorganisms.R

@@ -122,8 +122,8 @@ get_author_year <- function(ref) {
   authors <- gsub("[A-Z-][a-z-]?[.]", "", authors, ignore.case = FALSE)
   # remove trailing and leading spaces
   authors <- trimws(authors)
-  # keep only the part after last 'emend.' to get the latest authors
-  authors <- gsub(".*emend[.] ?", "", authors)
+  # strip emend. and everything after it to retain the combination authority
+  authors <- gsub(" ?emend[.]?.*", "", authors)
   # only keep first author and replace all others by 'et al'
   authors <- gsub("(,| and| et| &| ex| emend\\.?) .*", " et al.", authors)
   # et al. always with ending dot