[FEATURE] Auto-approve Write/Edit tools after plan approval in plan mode

Description

When using plan mode workflow (EnterPlanMode → ExitPlanMode → implementation), it creates a redundant user experience where:

1. User reviews and approves the implementation plan via ExitPlanMode
2. During implementation, Claude asks for permission again to create new files (Write tool)

This double confirmation feels redundant - if the user has already approved the plan that explicitly mentions file creation, they shouldn't need to approve each individual file creation again.

Proposed Solution

Add a new permission scope that applies only after plan approval:

Option A: Plan-scoped permissions

{
  "permissions": {
    "allow": ["Read", "Glob", "Grep"],
    "allowAfterPlanApproval": ["Write", "Edit"]
  }
}

Option B: Session state-based permissions

• When ExitPlanMode is approved, temporarily auto-approve Write/Edit tools until the next EnterPlanMode or /clear
• No configuration needed - intelligent default behavior

Related Issues

• #14259 PrePlanMode/PostPlanMode hooks (similar concept)
• #19874 Plan mode tool-level enforcement

Use Case

Japanese development workflow where:

• Plan creation and review is thorough (requirements.md, design.md, task.md)
• Once plan is approved, implementation should flow smoothly without interruption
• Current behavior breaks the flow with permission prompts

Current Workaround

Add "Write" to global allow list, but this removes safety checks outside of plan mode.

Environment

• Platform: macOS
• Claude Code version: latest