Format multi-day goal durations in the TUI (#20558)

## Why

Goal mode shows elapsed time in compact hour/minute form. That is easy
to scan for shorter runs, but once a goal runs past 24 hours, large hour
counts become harder to read at a glance.

## What changed

Updated `codex-rs/tui/src/goal_display.rs` so unbudgeted goal elapsed
time keeps the existing compact format below one day, then switches to a
day-aware format once the elapsed time reaches 24 hours:

- `23h 59m`
- `1d 0h 0m`
- `2d 23h 42m`

The formatter now covers the 24-hour boundary in unit tests, and the TUI
status-line snapshot for a completed elapsed goal now exercises the
multi-day display.

## Verification

- `cargo test -p codex-tui`

Here's my longest-running test task:

<img width="186" height="23" alt="image"
src="https://github.com/user-attachments/assets/cedfcdab-7f6e-44e6-8495-8a39f63973fb"
/>

codex-rs/tui/src/chatwidget/snapshots/codex_tui__chatwidget__tests__status_line_goal_complete_elapsed_footer.snap

@@ -6,4 +6,4 @@ expression: normalized_backend_snapshot(terminal.backend())
 "                                                                                "
 "› Ask Codex to do anything                                                      "
 "                                                                                "
-"  gpt-5.4                                                  Goal achieved (30m)  "
+"  gpt-5.4                                           Goal achieved (2d 23h 42m)  "

codex-rs/tui/src/chatwidget/tests/status_and_layout.rs

@@ -1626,16 +1626,18 @@ async fn status_line_goal_complete_elapsed_footer_snapshot() {
     chat.show_welcome_banner = false;
     chat.config.tui_status_line = Some(vec!["model-name".to_string()]);
     chat.refresh_status_line();
+    let mut goal = test_thread_goal(
+        codex_app_server_protocol::ThreadGoalStatus::Complete,
+        /*token_budget*/ None,
+        /*tokens_used*/ 40_000,
+    );
+    goal.time_used_seconds = 2 * 24 * 60 * 60 + 23 * 60 * 60 + 42 * 60;
     chat.handle_server_notification(
         ServerNotification::ThreadGoalUpdated(
             codex_app_server_protocol::ThreadGoalUpdatedNotification {
                 thread_id: "thread-1".to_string(),
                 turn_id: None,
-                goal: test_thread_goal(
-                    codex_app_server_protocol::ThreadGoalStatus::Complete,
-                    /*token_budget*/ None,
-                    /*tokens_used*/ 40_000,
-                ),
+                goal,
             },
         ),
         /*replay_kind*/ None,