Merge PR #520 from NikitkaRa: Insert: Summary, Section and Slide Zoom with Return to Zoom

Fix-ups in the merge (review): zoom targets, sections and titles are looked up with get()
instead of indexing; Hyperlink literals carry both main's sound fields and zoom_return;
duplicated test statements left by the test-file union are removed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/tests/show_clicks.rs

@@ -20,7 +20,14 @@ fn shape(p: &mut Presentation, name: &str, text: &str, x: f64, y: f64, w: f64, h
 }
 
 fn link_to(slide: SlideId) -> Option<Hyperlink> {
-    Some(Hyperlink { action: Action::Slide { slide }, tooltip: String::new(), highlight_click: false, sound: None, stop_sound: false })
+    Some(Hyperlink {
+        action: Action::Slide { slide },
+        tooltip: String::new(),
+        highlight_click: false,
+        sound: None,
+        stop_sound: false,
+        zoom_return: None,
+    })
 }
 
 /// Clicking `trigger` makes `target` disappear.