fix: support large files in comparisons

Replace the 16 MiB comparison rejection with independent bounded per-side loading and frozen Working blobs. Bound diff computation, defer large inline highlighting, index source-row navigation, and expose actual load failures. Verified the real 52.3 MB parser through repository/session APIs and terminal rendering with EOF/start navigation.

src/tui.rs

@@ -3976,13 +3976,21 @@ impl WheelPanels {
         } else {
             let content = diff_pane_panel(frame, diff, selected, panes, true, resolver);
             frame.render_widget(
-                Paragraph::new(if diff.loading {
+                Paragraph::new(display_text(if diff.loading {
                     "Loading file…"
+                } else if let Some(error) = diff.error.as_deref() {
+                    error
                 } else if selected.is_some() {
                     "File details unavailable · select the file to retry"
                 } else {
                     "No changed files"
-                }),
+                }))
+                .wrap(Wrap { trim: false })
+                .style(Style::default().fg(if diff.error.is_some() {
+                    Color::Red
+                } else {
+                    Color::Reset
+                })),
                 content,
             );
         }