PM: html2pptx v3 - fix slide detection to direct children only

- deck.querySelectorAll('.ppt-slide') -> deck.querySelectorAll(':scope > .ppt-slide')
  prevents nested .ppt-slide elements from being counted as separate slides
- Enhanced visibility filter: check opacity, display, visibility in addition to rect size
- Tested: dashi-deck.html now returns 14 slides (was 20), simple.html returns 10

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

bin/html2pptx.js

@@ -158,7 +158,7 @@ async function main() {
       // DashiAI format: .ppt-deck > .ppt-slide
       var deck = document.querySelector('.ppt-deck');
       if (deck) {
-        slides = deck.querySelectorAll('.ppt-slide');
+        slides = deck.querySelectorAll(':scope > .ppt-slide');
       }
       if (!slides || slides.length <= 1) {
         slides = document.querySelectorAll(
@@ -170,7 +170,11 @@ async function main() {
       }
       slides = Array.from(slides).filter(function (s) {
         var r = s.getBoundingClientRect();
-        return r.width > 0 && r.height > 0;
+        var style = window.getComputedStyle(s);
+        return r.width > 0 && r.height > 0 &&
+               style.opacity !== '0' &&
+               style.display !== 'none' &&
+               style.visibility !== 'hidden';
       });
 
       // Tags whose full text content should be a single text box