Fix {.help} markup to use correct cli link format [{.fun fn}](AMR::fn)

Replace all instances of {.help AMR::fn}() (incorrect format with manual
parentheses outside the link) with {.help [{.fun fn}](AMR::fn)} which is
the correct cli hyperlink syntax: the display text [{.fun fn}] renders the
function name with parentheses automatically, and (AMR::fn) is the link target.

Also update the plain-text fallback handler in aa_helper_functions.R to
extract the display text from the [text](topic) markdown link format,
so that non-cli environments show just the function name (e.g. `fn()`),
not the raw link markup.

Dynamic cases in amr_selectors.R and mo_property.R also updated.

https://claude.ai/code/session_01XHWLohiSTdZvCutwD7ag2b

R/atc_online.R

@@ -180,7 +180,7 @@ atc_online_property <- function(atc_code,
       colnames(out) <- gsub("^atc.*", "atc", tolower(colnames(out)))
 
       if (length(out) == 0) {
-        message_("in {.help AMR::atc_online_property}(): no properties found for ATC ", atc_code[i], ". Please check {.href {atc_url} this WHOCC webpage}.")
+        message_("in {.help [{.fun atc_online_property}](AMR::atc_online_property)}: no properties found for ATC ", atc_code[i], ". Please check {.href {atc_url} this WHOCC webpage}.")
         returnvalue[i] <- NA
         next
       }