Qualify all {.help} tags with AMR:: and convert backtick ?func references

- Add AMR:: namespace prefix and trailing () to all {.help} cli markup
  so they render as clickable help links (e.g. {.help AMR::as.sir}())
- Convert `?funcname` backtick-quoted help references to {.help AMR::funcname}()
  in aa_helper_functions.R, custom_eucast_rules.R, interpretive_rules.R,
  key_antimicrobials.R, mo.R, plotting.R, resistance_predict.R, and sir.R
- Skipped `?proportion` in sir_calc.R as 'proportion' is not exported

https://claude.ai/code/session_01XHWLohiSTdZvCutwD7ag2b

R/resistance_predict.R

@@ -238,7 +238,7 @@ resistance_predict <- function(x,
     prediction <- predictmodel$fit
     se <- predictmodel$se.fit
   } else {
-    stop("no valid model selected. See `?resistance_predict`.")
+    stop("no valid model selected. See {.help AMR::resistance_predict}().")
   }
 
   # prepare the output dataframe