Add {.topic} markup for non-function help page references

Replace {.code ?AMR-options} and backtick-style ?AMR-options / ?AMR-deprecated
references with proper {.topic AMR-options} / {.topic AMR-deprecated} cli markup
in count.R, interpretive_rules.R, proportion.R, and zz_deprecated.R.

Add {.topic} fallback handler to format_message() in aa_helper_functions.R:
plain-text environments render {.topic foo} as ?foo, and the [text](topic)
link form extracts just the display text (same pattern as {.help}).

Also convert remaining backtick function/arg references in proportion.R to
{.help [{.fun ...}](AMR::...)}, {.arg}, and {.code} markup for consistency.

Note: zzz.R intentionally keeps the backtick form since its startup message
goes through packageStartupMessage() which bypasses our cli infrastructure.

https://claude.ai/code/session_01XHWLohiSTdZvCutwD7ag2b

R/zz_deprecated.R

@@ -124,7 +124,7 @@ deprecation_warning <- function(old = NULL, new = NULL, fn = NULL, extra_msg = N
           ". The old name will be removed in future version, so please update your code.",
           ifelse(type == "argument",
             ". While the old argument still works, it will be removed in a future version, so please update your code.",
-            " and will be removed in a future version, see `?AMR-deprecated`."
+            " and will be removed in a future version, see {.topic AMR-deprecated}."
           )
         ),
         ifelse(!is.null(extra_msg),