[Feature Request] Add preserveFullHeader option to keep welcome panels with custom statusLine

Bug Description
Feature Request: Option to preserve full welcome header when using custom statusLine

Current behavior:
When configuring a custom statusLine in settings.json, Claude Code switches to a simplified/compact header that only shows version, model, and path. The full welcome header with "Welcome back!", "Tips for getting started", and "Recent activity" panels is hidden.

Requested feature:
Add an option to preserve the full welcome header while using a custom status line:

"statusLine": {
"type": "command",
"command": "~/.claude/status-line.sh",
"preserveFullHeader": true
}

Use case:
I have a custom status line showing context window usage percentage with a progress bar. This is useful information that doesn't appear in the default header. However, I still want to see the welcome message, tips, and recent activity when starting a session - these provide helpful context that's different from what my status bar shows.

Suggestion:
Allow users to opt-in to keeping the full header, or make the simplified header opt-in instead (since users might not expect their header to change when adding a status line).

Environment Info

• Platform: darwin
• Terminal: vscode
• Version: 2.0.76
• Feedback ID: