data.fill and text.fit: fill copies of a frame from rows of data

- data.fill {id, rows, gap?, formats?, dir?, format?, scale?}: repeats a
  frame once per row in one undo step; each row key names layers in the
  copy (text, or {text?, fill?, visible?, fit?}). `formats` makes each row
  once per size (feed, story, square), the copy resized so its auto layout
  reflows. With `dir`, each copy is exported under a unique file name; a
  failed export is reported in `errors` and keeps the copies.
- text.fit {ids?, maxLines?, minSize?, orphans?}: the largest font size,
  down to a floor, at which fixed-width text stays within N lines and its
  box; avoids a one-word last line; `fits` comes from the final text.
- Plugins can't call data.fill: it runs other commands inside, past the
  plugin policy, like command.batch.

crates/engine/src/plugins.rs

@@ -111,6 +111,8 @@ const DENIED: &[&str] = &[
     "edit.redo",
     "edit.repeat",
     "command.batch",
+    // Runs other commands inside (duplicate, edit, export), past this policy, like a batch.
+    "data.fill",
     // Network sessions, online files and their recovery copies on disk.
     "collab.",
     // Opens files in new windows.