refactor(gnerative-ai): migrate batch 2 generative-ai samples to @google/genai

[angelcaamal]

Description

Fixes Internal: b/519970318

Note: Before submitting a pull request, please open an issue for discussion if you are not associated with Google.

Checklist

• I have followed guidelines from CONTRIBUTING.MD and Samples Style Guide
• Tests pass: npm test (see Testing)
• Lint pass: npm run lint (see Style)
• Required CI tests pass (see CI testing)
• These samples need a new API enabled in testing projects to pass (let us know which ones)
• These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• This pull request is from a branch created directly off of GoogleCloudPlatform/nodejs-docs-samples. Not a fork.
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• This sample adds a new sample directory, and I created GitHub Actions workflow for this sample
• This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• Please merge this PR for me once it is approved

Note: Any check with (dev), (experimental), or (legacy) can be ignored and should not block your PR from merging (see CI testing).

[gemini-code-assist]

Code Review

This pull request migrates several Gemini Node.js snippets from the legacy @google-cloud/vertexai SDK to the new @google/genai SDK, updating the default model to gemini-2.5-flash and enabling the corresponding test suites. Feedback was provided on gemini-translate.test.js to add a fallback value for process.env.LOCATION to prevent test failures when the environment variable is not set.

[snippet-bot]

Here is the summary of changes.

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• generative-ai/snippets/gemini-translate.js:16, tag generativeaionvertexai_gemini_translate

You are about to delete 1 region tag.

• generative-ai/snippets/gemini-translate.js:18, tag generativeaionvertexai_gemini_translate

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[amcolin]

Changes look solid to me!