Modernise messaging infrastructure with cli support

Rewrites message_(), warning_(), stop_() to use cli::cli_inform(),
cli::cli_warn(), and cli::cli_abort() when the cli package is available,
with a fully functional plain-text fallback for environments without cli.

Key changes:
- New cli_to_plain() helper converts cli inline markup ({.fun}, {.arg},
  {.val}, {.field}, {.cls}, {.pkg}, {.href}, {.url}, etc.) to readable
  plain-text equivalents for the non-cli fallback path
- word_wrap() simplified: drops add_fn, ANSI re-index algorithm, RStudio
  link injection, and operator spacing hack; returns pasted input unchanged
  when cli is available
- stop_() no longer references AMR_env$cli_abort; uses pkg_is_available()
  directly; passes sys.call() objects to cli::cli_abort() call= argument
- Removed add_fn parameter from message_(), warning_(), and word_wrap()
- All call sites across R/ updated: add_fn arguments removed, some paste0-
  based string construction converted to cli glue syntax ({.fun as.mo},
  {.arg col_mo}, {n} results, etc.)
- cli already listed in Suggests; no DESCRIPTION dependency changes needed

https://claude.ai/code/session_01XHWLohiSTdZvCutwD7ag2b

R/atc_online.R

@@ -105,7 +105,6 @@ atc_online_property <- function(atc_code,
 
   if (!has_internet()) {
     message_("There appears to be no internet connection, returning NA.",
-      add_fn = font_red,
       as_note = FALSE
     )
     return(rep(NA, length(atc_code)))
@@ -181,7 +180,7 @@ atc_online_property <- function(atc_code,
       colnames(out) <- gsub("^atc.*", "atc", tolower(colnames(out)))
 
       if (length(out) == 0) {
-        message_("in `atc_online_property()`: no properties found for ATC ", atc_code[i], ". Please check ", font_url(atc_url, "this WHOCC webpage"), ".")
+        message_("in {.fun atc_online_property}: no properties found for ATC ", atc_code[i], ". Please check {.href {atc_url} this WHOCC webpage}.")
         returnvalue[i] <- NA
         next
       }