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/plotting.R

@@ -412,7 +412,7 @@ create_scale_sir <- function(aesthetics, colours_SIR, language, eucast_I, ...) {
 
   scale$labels <- function(x) {
     stop_ifnot(all(x %in% c(levels(NA_sir_), "SI", "IR", NA)),
-      "Apply `scale_", aesthetics[1], "_sir()` to a variable of class 'sir', see {.help AMR::as.sir}().",
+      "Apply `scale_", aesthetics[1], "_sir()` to a variable of class 'sir', see {.help [{.fun as.sir}](AMR::as.sir)}.",
       call = FALSE
     )
     x <- as.character(x)