Fix sr-only text leaking visually in template builder

The page.vue component uses container-type: size for CSS container
queries. This containment context interferes with the clip: rect(0,0,0,0)
technique used by Tailwind's sr-only class, causing the hidden page text
to render visually below the PDF image.

Replace sr-only class with position: absolute; left: -9999px off-screen
technique which is robust against CSS containment contexts.

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

app/javascript/template_builder/page.vue

@@ -17,7 +17,7 @@
     >
     <div
       v-if="pageText"
-      class="sr-only"
+      style="position: absolute; left: -9999px; width: 1px; height: 1px; overflow: hidden;"
       :aria-label="`Page ${number + 1} text content`"
     >
       {{ pageText }}