documents: lists go on, block lines shift, tables change, matches show, fences color by language

The document carries Markdown's editing tools for ElyMark (MARK-06):
Enter continues a list item or ends an empty one, Tab and Shift-Tab
shift an open block's lines, table rows and columns come and go as
one undo step, a match shows in any mode, replacements are one step,
and a fenced block colors by its language.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/forms/mod.rs

@@ -113,7 +113,7 @@ pub use structure::{
     DirtyIndicator, Form, FormError, FormField, FormLabel, FormSection, InlineForm,
 };
 pub use switch::Switch;
-pub(crate) use syntax::{Syntax, syntax_of};
+pub(crate) use syntax::{Syntax, syntax_fenced, syntax_of};
 pub use tags::TagInput;
 pub(crate) use text::{
     Backspace, Copy, Cut, Delete, DeleteWordLeft, Down, Enter, Redo, Submit, Undo, Up, bind_keys,