docs: Update agents.mdx / models section w/ correct provider/model-id format

[bdwelle]

Previous version incorrectly stated "The model ID in your OpenCode config uses the format provider/model-id. For example, if you’re using OpenCode Zen, you would use opencode/gpt-5.1-codex for GPT 5.1 Codex."

This commit corrects the provider/model-id format and examples. The provider indeed prefixes the model-id, but it's the full model-id, not just the part to the right of the slash, e.g.

opencode/openai/gpt-5.1-codex
openai/openai/gpt-5.1-codex

What does this PR do?

corrects incorrect/confusing documentation

How did you verify your code works?

tested in opencode.json

[github-actions]

Hey! Your PR title Update agents.mdx ### models w/ correct provider/model-id format 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:

No duplicate PRs found