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/render/blocks.rs

@@ -143,7 +143,7 @@ impl Draw<'_> {
                     4 => entry.pl_16(),
                     _ => entry.pl_20(),
                 };
-                let Some(reveal) = self.on_heading.clone() else {
+                let Some(reveal) = self.hooks.on_heading.clone() else {
                     return entry.text_color(colors.fg_muted).into_any_element();
                 };
                 let (at, pressed) = (heading.at, reveal.clone());