tui: • Working, 100% context dim (#4629)

- add a `•` before the "Working" shimmer
- make the percentage in "X% context left" dim instead of bold

<img width="751" height="480" alt="Screenshot 2025-10-02 at 2 29 57 PM"
src="https://github.com/user-attachments/assets/cf3e771f-ddb3-48f4-babe-1eaf1f0c2959"
/>

codex-rs/tui/src/status_indicator_widget.rs

@@ -160,7 +160,7 @@ impl WidgetRef for StatusIndicatorWidget {
         let pretty_elapsed = fmt_elapsed_compact(elapsed);
 
         // Plain rendering: no borders or padding so the live cell is visually indistinguishable from terminal scrollback.
-        let mut spans = vec!["  ".into()];
+        let mut spans = vec!["• ".dim()];
         spans.extend(shimmer_spans(&self.header));
         spans.extend(vec![
             " ".into(),