feat: improve page highlight with orange color and template grouping

- Add --color-page-highlight CSS variable (#ff8a50)
- Change page edge highlight from blue to orange
- Keep border visible while PagePopup is open
- Highlight all pages using the same template (data-page-type)
- Display dynamic page count in PagePopup header
- Emit close event from PagePopup for proper cleanup

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

public/assets/css/src/_variables.scss

@@ -4,6 +4,8 @@
   --color-browngray-200: #d0c4ba;
   --color-browngray-300: #b5a9a1;
 
+  --color-page-highlight: #ff8a50;
+
   --border-radius: 0.2rem;
 
   --space-xs: 0.5rem;