fix(css): wrap address-book-index.css in @layer pages block

css-contract-check.sh expects @layer pages { (block syntax),
not @layer pages; (statement syntax) — regex captures up to
the first whitespace or { so the semicolon was included in the
detected layer name.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

modules/addressbook/web/css/pages/address-book-index.css

@@ -1,4 +1,4 @@
-@layer pages;
+@layer pages {
 
 /* Address book list — dense identity layout */
 
@@ -143,3 +143,5 @@
     max-width: 100%;
   }
 }
+
+} /* end @layer pages */