docs: fix logging example for plugin

[tlinhart]

What does this PR do?

It fixes the example for logging from a plugin. According to the SDK documentation (https://opencode.ai/docs/sdk#examples-1), the fields need to be wrapped in a top-level body field.

How did you verify your code works?

I tried to create a plugin and checked which approach works.

[github-actions]

Hey! Your PR title Fix logging example for plugin doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Potential Duplicate Found:

• PR fix(docs): update logging example in plugin #10473: "fix(docs): update logging example in plugin"
  • fix(docs): update logging example in plugin #10473
  • Reason: This PR appears to address the same issue - updating/fixing the logging example in plugins. Since PR docs: fix logging example for plugin #11989 is also fixing a logging example for plugins, this could be a duplicate or related fix. You may want to check if fix(docs): update logging example in plugin #10473 was already merged or if it addresses the same body field wrapping issue.