acp: permission request flow for tool execution

[bug-ops]

Parent: #762

Task

Implement session/request_permission flow: before executing sensitive tools, ask the IDE user for approval.

Acceptance criteria

• Map tool kinds to permission categories (read, edit, delete, execute)
• Send session/request_permission with permission options (allow_once, allow_always, reject_once, reject_always)
• Cache allow_always / reject_always decisions per session
• Handle cancellation (user dismisses permission dialog)
• Integrate with existing Channel::confirm() pattern
• Skip permission requests for read-only operations if client capabilities indicate auto-approve