Default Guardian v2 to computer-use reviews with images (#40846)

## What changed

- Default Guardian v2's review scope to computer-use tools. Set
  `features.guardianv2.review_scope.computer_use_only = false` to retain the
  broader tool review scope.
- Include images in Guardian transcripts by default. Set
  `features.guardianv2.transcript.include_images = false` to disable them.

## Testing

- Update configuration and app-server coverage for the new defaults and
  explicit broader-scope overrides.

GitOrigin-RevId: 88c3cfe6dd2a96df052111794ad59c5c9ea39b78