docs(template-require-mandatory-role-attributes): cite HTML-AAM as primary source

axobject-query is the data package the rule queries, but the normative
source for "native <input type=checkbox> exposes aria-checked via the
checked IDL attribute" is HTML-AAM §el-input-checkbox. Adding the HTML-AAM
link makes the exemption's spec grounding explicit instead of leaving
axobject-query as a free-floating data source.

Author: johanrd

docs/rules/template-require-mandatory-role-attributes.md

@@ -62,4 +62,8 @@ Un-documented pairings (e.g. `<input type="checkbox" role="menuitemcheckbox">` 
 
 - [WAI-ARIA Roles](https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Roles)
 - [WAI-ARIA APG — Switch pattern](https://www.w3.org/WAI/ARIA/apg/patterns/switch/)
-- [axobject-query](https://github.com/A11yance/axobject-query) — AX-tree data source for the exemption lookup
+- [HTML-AAM — `<input type="checkbox">` → `checkbox` role mapping](https://www.w3.org/TR/html-aam-1.1/#el-input-checkbox)
+  — primary-spec source: the native element's accessibility mapping supplies
+  the required ARIA state via the `checked` IDL attribute, which is what
+  axobject-query encodes.
+- [axobject-query](https://github.com/A11yance/axobject-query) — AX-tree data source for the exemption lookup (secondary, encodes HTML-AAM)