docs(GH-18778): Fixes .opencode/tools references in docs

[divinedragon]

Issue for this PR

Closes #18778

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Fixes incorrect .opencode/tools under custom tools section in the documentation.

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How did you verify your code works?

This is a change in the documentation

Screenshots / recordings

No UI change.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

If you do not follow this template your PR will be automatically rejected.

[github-actions]

Hey! Your PR title GH-18778: Fixes .opencode/tools references in docs 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.