fix(session_picker): stronger highlight on the selected row in dark terminals

The `/sessions` picker's selection background was subtle enough
to disappear in low-contrast dark themes — keyboard navigation
moved the focus indicator but the visual change between focused
and unfocused rows was hard to notice, especially when running
the TUI in a terminal with a near-black background.

The selected row now renders with a bolded label on a stronger
background so the focused row reads cleanly across the dark
palettes the TUI ships with. The non-selected rows are unchanged
so the change doesn't add visual noise on light terminals.

Test pin: `build_list_lines_selected_row_uses_strong_highlight`
ensures the rendered row at the selected index applies the
expected modifier and background combination.

Harvested from PR #1493 by @reidliu41

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -16,6 +16,13 @@ real world uses."
 
 ### Fixed
 
+- **`/sessions` picker highlights the selected row more strongly
+  in dark terminals** (harvested from PR #1493 by **@reidliu41**).
+  Previously the selection background was subtle enough to lose
+  in low-contrast dark themes; keyboard navigation up/down didn't
+  obviously change which row was active. The selected row now
+  uses a bolded label on a stronger background so the focused row
+  reads cleanly across the dark palettes the TUI ships with.
 - **TUI input no longer freezes while long-running shell jobs
   flood stdout** (#1299, harvested from PR #1494 by
   **@CrepuscularIRIS / autoghclaw**). The job-panel refresh path

crates/tui/src/tui/session_picker.rs

@@ -491,7 +491,8 @@ fn build_list_lines(
         let style = if idx == selected {
             Style::default()
                 .fg(palette::SELECTION_TEXT)
-                .bg(palette::SELECTION_BG)
+                .bg(palette::DEEPSEEK_BLUE)
+                .add_modifier(Modifier::BOLD)
         } else {
             Style::default().fg(palette::TEXT_PRIMARY)
         };
@@ -771,6 +772,32 @@ mod tests {
         }
     }
 
+    #[test]
+    fn build_list_lines_selected_row_uses_strong_highlight() {
+        let sessions = vec![
+            test_session(1, "first session"),
+            test_session(2, "second session"),
+        ];
+        let lines = build_list_lines(&sessions, 1, 80, 0, 5, false, "", "recent", false, None);
+
+        let selected_line = lines
+            .iter()
+            .find(|line| {
+                line.spans
+                    .iter()
+                    .any(|span| span.content.contains("second session"))
+            })
+            .expect("selected session should render");
+        let span = selected_line
+            .spans
+            .first()
+            .expect("selected row should have a span");
+
+        assert_eq!(span.style.fg, Some(palette::SELECTION_TEXT));
+        assert_eq!(span.style.bg, Some(palette::DEEPSEEK_BLUE));
+        assert!(span.style.add_modifier.contains(Modifier::BOLD));
+    }
+
     #[test]
     fn ensure_selected_visible_updates_scroll_window() {
         let sessions = (0..10)