documents: a press opens its block on the pressed character; a secondary press points

Each drawn text piece keeps its written span, so a press maps back to a
source byte. A secondary press opens nothing: it moves the caret there and
emits DocumentEvent::Pointed with the block's kind, link, picture and
whether it lies in a table or code. Block nodes count from their own start.

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

src/documents/mod.rs

@@ -36,8 +36,8 @@ pub use counts::{ReadingTime, WordCount};
 pub use diagram::{Diagram, diagram_svg};
 pub(crate) use diagram::{flatten, options as svg_options};
 pub use document::{
-    Attachment, DocumentEvent, DocumentHeading, DocumentLook, LARGEST_READ, MarkdownDocument,
-    TableEdit, TableRefusal,
+    Attachment, DocumentEvent, DocumentHeading, DocumentLook, DocumentTarget, LARGEST_READ,
+    MarkdownDocument, TableEdit, TableRefusal, TargetBlock,
 };
 pub use epub::{Chapter, EpubReader};
 pub use format::{Format, format};