[Feature Request] Allow suppressing additionalContext feedback display in Stop hooks

When a Stop hook returns additionalContext via hookSpecificOutput, Claude Code always displays it to the user:

● Ran N stop hooks
  ⎿  Stop hook feedback: <additionalContext value>

This is fine for hooks that want the user to see the injected context. But for background automation hooks — where additionalContext is intended only for Claude's next turn, not the user — there's no way to suppress this display.

suppressOutput: true only hides stdout, not the additionalContext feedback rendering.

Requested: A field (e.g. suppressFeedback: true on hookSpecificOutput, or extending suppressOutput to cover additionalContext) that allows a hook to inject context silently.

Use case: A Stop hook that silently injects a checkpoint reminder every N turns to trigger a background handoff update. The reminder is meant for Claude only — showing it to the user interrupts the conversation flow and exposes implementation details.