M7: area type auto size and shrink text to fit

Area Type Options gain a fit: none, autoHeight (Illustrator's Auto Size:
the frame's height follows the text after every edit, resolved in
refresh_bounds inside the edit so it shares the edit's undo step) and
shrinkText {minPercent} (beyond Illustrator: overflowing text scales its
sizes, leading and baseline shifts down at layout time by the largest
factor, in 0.1 pt steps of the first run, that fits). The Auto Size New
Area Type preference now applies. text.areaOptions and document.inspect
report overflow and the shrink factor; the Area Type Options dialog
offers fit and first baseline as dropdowns.

crates/engine/src/cmd/threads.rs

@@ -93,6 +93,16 @@ pub(crate) fn reflow(before: &Document, doc: &mut Document) {
             continue;
         }
         vectorcraft_text::edit::normalize(&mut story);
+        if live.len() >= 2 {
+            // Threaded frames keep their size: Auto Size is off for them (as in Illustrator).
+            for id in &live {
+                if text_of(doc, *id).is_some_and(|t| t.area.fit == vectorcraft_doc::AreaFit::AutoHeight)
+                    && let Some(NodeKind::Text(t)) = doc.node_mut(*id).map(|n| &mut n.kind)
+                {
+                    t.area.fit = vectorcraft_doc::AreaFit::None;
+                }
+            }
+        }
         let frames: Vec<TextObject> = live.iter().filter_map(|id| text_of(doc, *id).cloned()).collect();
         let refs: Vec<&TextObject> = frames.iter().collect();
         let parts = vectorcraft_text::thread::distribute(vectorcraft_text::FontDb::global(), &refs, &story);