feat(tui2): add multi-click transcript selection (#8471)

Support multi-click transcript selection using transcript/viewport
coordinates
(wrapped visual line index + content column), not terminal buffer
positions.

Gestures:
- double click: select word-ish token under cursor
- triple click: select entire wrapped line
- quad click: select paragraph (contiguous non-empty wrapped lines)
- quint+ click: select the entire history cell (all wrapped lines
belonging to a
  single `HistoryCell`, including blank lines inside the cell)

Selection expansion rebuilds the wrapped transcript view from
`HistoryCell::display_lines(width)` so boundaries match on-screen
wrapping during
scroll/resize/streaming reflow. Click grouping is resilient to minor
drag jitter
(some terminals emit tiny Drag events during clicks) and becomes more
tolerant as
the sequence progresses so quad/quint clicks are practical.

Tests cover expansion (word/line/paragraph/cell), sequence resets
(timing, motion,
line changes, real drags), drag jitter, and behavior on spacer lines
between
history cells (paragraph/cell selection prefers the cell above).

codex-rs/tui2/src/markdown_render.rs

@@ -468,11 +468,19 @@ where
             .indent_stack
             .iter()
             .any(|ctx| ctx.prefix.iter().any(|s| s.content.contains('>')));
-        let style = if blockquote_active {
+        let mut style = if blockquote_active {
             self.styles.blockquote
         } else {
             line.style
         };
+        // Code blocks are "preformatted": we want them to keep code styling even when they appear
+        // within other structures like blockquotes (which otherwise apply a line-level style).
+        //
+        // This matters for copy fidelity: downstream copy logic uses code styling as a cue to
+        // preserve indentation and to fence code runs with Markdown markers.
+        if self.in_code_block {
+            style = style.patch(self.styles.code);
+        }
         let was_pending = self.pending_marker_line;
 
         self.current_initial_indent = self.prefix_spans(was_pending);