Add external action permission scopes

[FanyinLiu]

Summary

• add once, current-session, and persistent grant scopes for main-process external action confirmations
• keep session grants in memory while persistent grants promote the integration to auto mode
• record grant scope metadata without logging message text, commands, target IDs, or tool arguments

Verification

• npm test -- tests/external-action-policy.test.ts tests/external-action-audit.test.ts
• npx tsc -b --pretty false
• npm run error-redaction:audit
• npm run lint
• git diff --check
• npm run verify:pr