[Bug] Update notification wraps vertically, breaking statusline layout

Description

When the "Update available! Run: brew upgrade claude-code" notification is displayed on the right side of the statusline, it wraps character-by-character vertically instead of being truncated, hidden or shown in a new line when there isn't enough horizontal space. This makes the entire right side of the terminal unusable.

The notification itself is also a false positive — brew upgrade claude-code reports "the latest version is already installed" (related: #19905, #18047).

Screenshot

<img width="441" height="800" alt="Image" src="https://github.com/user-attachments/assets/ca064b29-629f-4246-8332-c70f20c7075b" />

Steps to Reproduce

1. Install Claude Code via Homebrew (already on latest version)
2. Configure a custom statusline script via settings.json that outputs ~70+ characters
3. Launch Claude Code — the "Update available" notification appears on the right
4. The notification text wraps vertically, one character per line, filling the entire right column

Expected Behavior

• The notification should be truncated, hidden, or rendered on a separate line when there isn't enough horizontal space
• Ideally, the notification should not appear at all when the latest version is already installed (see #19905)

Actual Behavior

The notification text "Update available! Run: brew upgrade claude-code" renders in a ~2-character-wide column on the right side, wrapping each character onto a new line. This spans the entire height of the terminal and is extremely distracting.

Environment

• Claude Code: 2.1.38
• Installation: Homebrew
• OS: macOS 26.2 (Tahoe)
• Terminal: Ghostty
• Terminal width: 80 columns
• Custom statusline: Yes (via settings.json → statusLine.command)