feat(opencode): support github ref plugins and config model limit overrides

[sjawhar]

Issue for this PR

Fixes#12143

Type of change

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

What does this PR do?

Support github:owner/repo#ref plugin specifiers in bun install. Resolves plugin install path for github-based dependencies and adds config-level model token limit overrides.

How did you verify your code works?

• Ran bun typecheck from packages/opencode
• Ran targeted unit tests
• Tested with custom binary build

Checklist

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

[github-actions]

Hey! Your PR title feat(bun,provider): support github ref plugins and config model limit overrides 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:

Based on my search results, I found one potentially related PR:

PR #16306 - fix(opencode): honor model limit.input overrides
#16306

This PR appears related because it addresses model limit overrides, which is one of the two main features in PR #20671. However, it's labeled as a fix rather than a new feature, suggesting it may have been addressing a bug rather than adding the full config-level override capability that PR #20671 implements.

The searches did not reveal any other PRs specifically addressing GitHub ref plugin support or comprehensive config-level model limit overrides that would duplicate PR #20671's functionality.

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍