fix(#48): address round-2 Copilot review (doc + test polish)

Author: johanrd

lib/rules/template-no-empty-headings.js

@@ -40,7 +40,7 @@ function isAriaHiddenTruthy(attr) {
       return value.path.value === true;
     }
     if (value.path.type === 'GlimmerStringLiteral') {
-      return value.path.value.toLowerCase() === 'true';
+      return value.path.value.trim().toLowerCase() === 'true';
     }
   }
   if (value.type === 'GlimmerConcatStatement') {
@@ -58,11 +58,11 @@ function isAriaHiddenTruthy(attr) {
           return only.path.value === true;
         }
         if (only.path.type === 'GlimmerStringLiteral') {
-          return only.path.value.toLowerCase() === 'true';
+          return only.path.value.trim().toLowerCase() === 'true';
         }
       }
       if (only.type === 'GlimmerTextNode') {
-        const chars = only.chars.toLowerCase();
+        const chars = only.chars.trim().toLowerCase();
         return chars === '' || chars === 'true';
       }
     }

tests/lib/rules/template-no-empty-headings.js

@@ -54,6 +54,15 @@ ruleTester.run('template-no-empty-headings', rule, {
     '<template><h1 aria-hidden="True"></h1></template>',
     '<template><h1 aria-hidden={{"TRUE"}}></h1></template>',
     '<template><h1 aria-hidden={{"True"}}></h1></template>',
+    // Quoted-mustache (GlimmerConcatStatement) forms — `aria-hidden="{{true}}"`
+    // resolves the same as `aria-hidden={{true}}`. Pin these so future
+    // refactors don't regress concat handling.
+    '<template><h1 aria-hidden="{{true}}"></h1></template>',
+    '<template><h1 aria-hidden="{{"true"}}"></h1></template>',
+    // Whitespace normalization — incidental surrounding whitespace should
+    // still resolve to "true".
+    '<template><h1 aria-hidden={{" true "}}></h1></template>',
+    '<template><h1 aria-hidden=" true "></h1></template>',
   ],
   invalid: [
     {