Feature request: Option to suppress "Async hook X completed" UI messages

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

When hooks are configured with async: true, Claude Code displays completion
messages like "⎿ Async hook PreToolUse completed" in the transcript.

Proposed Solution

Add a hook-level option (e.g. suppressCompletionMessage: true) or a
global setting to hide these messages while keeping the hooks active.

Alternative Solutions

_No response_

Priority

Low - Nice to have

Feature Category

CLI commands and flags

Use Case Example

Async hooks from plugins (e.g. everything-claude-code) generate several
of these messages per interaction, creating visual noise without adding useful
information to the conversation.

Additional Context

_No response_