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/key_antimicrobials.R

@@ -187,7 +187,7 @@ key_antimicrobials <- function(x = NULL,
           "No columns available ",
           paste0("Only using ", values_new_length, " out of ", values_old_length, " defined columns ")
         ),
-        "as key antimicrobials for ", name, "s. See {.help AMR::key_antimicrobials}()."
+        "as key antimicrobials for ", name, "s. See {.help [{.fun key_antimicrobials}](AMR::key_antimicrobials)}."
       )
     }