Context low banner hides custom statusline content

Bug Description

When context usage is high (90%+), the "Context low (X% remaining) · Run /compact" banner appears and overlays/hides custom statusline content. Multi-line statuslines lose their lower lines (e.g., issue references, position indicators) because the banner takes precedence in the rendering area.

Steps to Reproduce

1. Configure a multi-line custom statusline via settings.json → statusLine.command
2. Use a session until context reaches 90%+
3. Observe that the "Context low" banner replaces/covers the custom statusline output

Expected Behavior

The "Context low" banner should coexist with the custom statusline — either rendered above/below it, or integrated into the statusline's JSON input so users can handle it in their own script.

Actual Behavior

The banner overlays the statusline area, hiding lines 3+ of multi-line statusline output. Users lose visibility into session-specific state (issue tracking, position info) exactly when they need it most — at high context usage.

Possible Solutions

1. Render the banner as a separate UI element that doesn't overlap the statusline
2. Add a context_warning field to the statusline JSON input so custom scripts can render it themselves
3. Provide a setting to disable/configure the banner (e.g., "contextWarningBanner": false)

Environment

• Claude Code CLI (native install, macOS)
• Custom statusline via bash ~/.claude/statusline-command.sh
• Multi-line output (path, git+context+model, position, issue reference)