Add setting to suppress the recurring auto-mode explainer banner

Problem

When permissions.defaultMode: "auto" is set in ~/.claude/settings.json (or the session is launched with --permission-mode auto), Claude Code displays this multi-line explainer at the start of every session:

Auto mode lets Claude handle permission prompts automatically — Claude checks each tool call for risky actions and prompt injection before executing. Actions Claude identifies as safe are executed, while actions Claude identifies as risky are blocked and Claude may try a different approach. Ideal for long-running tasks. Sessions are slightly more expensive. Claude can make mistakes that allow harmful commands to run, it's recommended to only use in isolated environments. Shift+Tab to change mode.

For users who have already opted into auto mode as their default, this banner is redundant on every session — they understand the trade-offs and don't need the explainer repeated. The existing skipAutoPermissionPrompt: true setting suppresses the initial confirmation dialog but does not suppress this in-session explainer.

There appears to be no documented setting, env var, or CLI flag that hides just this banner.

Proposed solution

Add a setting (e.g. skipAutoModeBanner: true or hideAutoModeExplainer: true) under ~/.claude/settings.json that, when set, suppresses the recurring explainer text shown when entering auto mode. The Shift+Tab mode-change hint could still be surfaced elsewhere (or omitted for users who have explicitly opted in).

Behavior I'd expect:

• skipAutoModeBanner: false (default) — current behavior
• skipAutoModeBanner: true — banner is fully hidden; auto mode still activates normally

Environment

• Claude Code CLI, latest
• Linux (Ubuntu)
• permissions.defaultMode: "auto", skipAutoPermissionPrompt: true, skipDangerousModePermissionPrompt: true

Related

• #56956 — request to hide the status-bar auto mode on indicator (related but distinct: that's the persistent footer label; this is the multi-line in-conversation explainer)