fix(slide): drop trailing blank page in PDF export

The @media print rule applied `break-after: page` to every `.slide`, including
the last one, which produced an extra empty page (e.g. 4 pages for a 3-slide
deck). Reset the last slide to `break-after: auto` so page count equals slide
count. Verified: 3-slide deck → 3 pages, 1-slide deck → 1 page.

Co-Authored-By: First Fluke <our.first.fluke@gmail.com>

Author: gracefullight

.agents/skills/oma-slide/resources/assets/viewport-base.css

@@ -248,6 +248,12 @@
     break-after: page;
   }
 
+  /* No trailing blank page: the last slide must not force a page break. */
+  .slide:last-child {
+    page-break-after: auto;
+    break-after: auto;
+  }
+
   .slide.active,
   .slide.visible {
     z-index: auto;