fix: Bedrock model config update

[sfradkin]

Issue for this PR

Closes #

Type of change

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

What does this PR do?

This PR fixes our ability to use OpenCode with the following Bedrock models:

• Writer Palmyra X4
• Writer Palmyra X5
• DeepSeek R1 (A)
• Mistral Pixtral Large
• Meta Llama 4 Maverick 17B
• Meta Llama 4 Scout 17B
• Amazon Nova 2 Lite

This was done through a combination of some small code fixes plus configuration fixes (in LOCAL_AWS_SETUP.md).

How did you verify your code works?

I tested out the models with a simple prompt.

Screenshots / recordings

N/A

Checklist

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

[github-actions]

Hey! Your PR title Bedrock model config update 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]

This PR doesn't fully meet our contributing guidelines and PR template.

What needs to be fixed:

• No issue referenced. Please add Closes #<number> linking to the relevant issue.

Please edit this PR description to address the above within 2 hours, or it will be automatically closed.

If you believe this was flagged incorrectly, please let a maintainer know.

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.