documents: right presses keep a selection; Delete Image

A right press in a text field or the code editor keeps a selection it
lands in, else moves the caret. In visual mode a right press in the open
block keeps it open and emits Pointed, read apart from the whole text.
MarkdownDocument::delete_image removes the picture at the caret.

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

src/documents/document/visual.rs

@@ -72,8 +72,15 @@ impl MarkdownDocument {
         // Focus fades all but the reader's block.
         let faded = self.look.focus && editing_mode(self.mode) && ix != self.current_block(cx);
         let open = self.open.as_ref();
+        let point = cx.listener(|document, _: &MouseDownEvent, window, cx| {
+            window.prevent_default();
+            cx.stop_propagation();
+            document.point_open(cx);
+        });
         let field = |open: &super::Open| {
             div()
+                .debug_selector(|| "markdown-open".to_string())
+                .on_mouse_down(MouseButton::Right, point)
                 .text_size(body)
                 .px_3()
                 .py_2()