feat(models): add Gemini 3.6 Flash tiers and model pricing

[ganimalqudhaifi]

Summary

• Add cost metadata for Gemini 3.5 Flash, Gemini 3.1 Pro, Claude Sonnet 4.6, and Claude Opus 4.6.
• Add Gemini 3.6 Flash with low, medium, and high tiers.
• Map tiers to verified Antigravity backend enums.

Verification

• npm run typecheck
• npm run build
• npm run smoke:node-import

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.

[JoveYu]

@anthonyhaussman please add gemini 3.6 flash

[anthonyhaussman]

I have included the Gemini 3.6 Flash models in the pull request #24.

It can be used right now by setting it in the opencode configuration:

    "@anthonyhaussman/opencode-agy-auth@alpha",

in the plugin section.

I'm testing it to check if there's no regression and merge it + release it if everything is okay.

Thanks for the PR. 🙏

[anthonyhaussman]

I have merged the PR and pushed the new 1.1.5 version to the npm repository with the implementation of Gemini 3.6.

I am closing this PR. 🙏