[BUG] "update available" banner hides the session title in the TUI

Description

When a Claude Code update is available, the TUI displays an "update available" banner in the slot that normally shows the active session's title. This makes it impossible to tell which session you're in until the update is applied (or the banner is otherwise dismissed).

Repro

1. Run Claude Code in a terminal while an update is available.
2. Look at the slot where the session title is normally rendered.
3. Observe: it shows the update prompt instead of the session title.

Expected

The session title should remain visible. The update notice belongs in a separate slot (e.g. footer, status bar) or should rotate / collapse without clobbering the title.

Impact

• Hard to identify the current session, especially when juggling several.
• Forces running claude update just to recover navigation context.

Environment

• Claude Code TUI (CLI), macOS (Darwin 25.5.0)
• Reproducible whenever an update is available