Add spacing before composer footer hints (#3469)

<img width="647" height="82" alt="image"
src="https://github.com/user-attachments/assets/867eb5d9-3076-4018-846e-260a50408185"
/>

codex-rs/tui/src/chatwidget/snapshots/codex_tui__chatwidget__tests__chat_small_idle_h2.snap

@@ -3,4 +3,4 @@ source: tui/src/chatwidget/tests.rs
 expression: terminal.backend()
 ---
 "▌ Ask Codex to do anything              "
-" ⏎ send   ⌃J newline   ⌃T transcript   ⌃"
+"                                        "

codex-rs/tui/src/chatwidget/snapshots/codex_tui__chatwidget__tests__chatwidget_exec_and_status_layout_vt100_snapshot.snap

@@ -12,4 +12,5 @@ expression: visual
  Investigating rendering code (0s • Esc to interrupt)
 
 ▌Summarize recent commits
+
  ⏎ send   ⌃J newline   ⌃T transcript   ⌃C quit

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

@@ -6,5 +6,6 @@ expression: terminal.backend()
 " Analyzing (0s • Esc to interrupt)                                              "
 "                                                                                "
 "▌ Ask Codex to do anything                                                      "
+"                                                                                "
 " ⏎ send   ⌃J newline   ⌃T transcript   ⌃C quit                                  "
 "                                                                                "