Update available banner persists after upgrading to latest version via brew

Description

After upgrading Claude Code via brew upgrade claude-code, the "Update available! Run: brew upgrade claude-code" banner continues to appear even after exiting and restarting the CLI.

Steps to Reproduce

1. Run brew upgrade claude-code (upgraded from 2.1.80 → 2.1.81)
2. Confirm upgrade succeeded ("claude-code was successfully upgraded!")
3. Launch claude — shows v2.1.81
4. Quit and relaunch claude
5. Banner still shows: "Update available! Run: brew upgrade claude-code"
6. Running brew upgrade claude-code again says: "Not upgrading claude-code, the latest version is already installed"

Verification

• claude --version → 2.1.81
• brew list --cask --versions claude-code → 2.1.81
• brew info claude-code → confirms 2.1.81 is installed and latest formula version
• which -a claude → only /opt/homebrew/bin/claude (no conflicting npm install)

Expected Behavior

The update banner should not appear when the installed version matches the latest available version.

Environment

• Claude Code: v2.1.81 (brew cask)
• OS: macOS (Darwin 25.3.0)
• Homebrew: latest
• Install method: brew install claude-code (cask only, no npm)