feat(opencode): Requesty custom plugin with our own SDK, and dynamic model discovery

[requesty-JohnCosta27]

Issue for this PR

#30285
#16344

Closes: #30285
Closes: #16344

Type of change

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

What does this PR do?

• Uses /v1/models for model discovery with Requesty.
• Uses the @requesty/ai-sdk package instead of openai-compatible, there's another pending PR to update our models.dev entry: Updating Requesty models models.dev#3813

How did you verify your code works?

• Unit tests
• Testing with bun dev, and checking that using /models with Requesty brings up the correct number of models, including user policies, and filtering down to the users approved models.

Screenshots / recordings

Checklist

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

[github-actions]

Hey! Your PR title Requesty custom plugin + Model discovery 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]

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