Support Gemini 2.5 model family with Google GenAI client

[mcndt]

why

I want to use the latest Gemini 2.5 models.

what changed

I updated the list of available models and mapping to model provider to include the following models:

• Gemini 2.5 Flash
• Gemini 2.5 Flash (September 2025 Preview)
• Gemini 2.5 Flash Lite
• Gemini 2.5 Flash Lite (September 2025 Preview)
• Gemini 2.5 Pro

test plan

Works out of the box with the Google GenAI client.

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 1fe80de7342128aee1a29b5a76725294551a78c8

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@browserbasehq/stagehand	Patch
@browserbasehq/stagehand-evals	Patch

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[miguelg719]

hey @mcndt , thanks for the contrib! Before merging, can you try set the modelName to google/<2.5-family-modelname> and see if it works/supports your config? We're adopting AI SDK more for LLM inference to avoid custom client maintenance

[mcndt]

Rebased this branch on the 3.0.1 release

[mcndt]

@miguelg719 I verified that the model names would indeed be compatible with the AI SDK!