fix(gemini): refresh AI Studio model fallback

[wilsonicdev]

Fixes #3231.

Summary

• refresh the Gemini (Google AI Studio) static fallback so the provider tab exposes current 3.x models
• include Gemini 2.5 fallback entries while preserving the existing gemini-2.0-flash default ordering
• strengthen the model catalog regression test to assert the AI Studio fallback includes the current models

Tests

• node --import tsx/esm --test tests/unit/t28-model-catalog-updates.test.ts tests/unit/executor-default-base.test.ts tests/unit/provider-models-config.test.ts
• node --import tsx/esm -e 'const { getDefaultModel, getModelsByProviderId } = await import("./open-sse/config/providerModels.ts"); console.log("default", getDefaultModel("gemini")); console.log(getModelsByProviderId("gemini").slice(0,10).map(m=>m.id));'\n- git diff --check

[gemini-code-assist]

Code Review

This pull request updates the Gemini model catalog in open-sse/config/providerRegistry.ts by adding several new Gemini models, including Gemini 3.1 Pro Preview, Gemini 3 Flash Preview, Gemini 3.1 Flash Lite Preview, Gemini 3.5 Flash, Gemini 2.5 Pro, Gemini 2.5 Flash, and Gemini 2.5 Flash Lite. Additionally, the unit test in tests/unit/t28-model-catalog-updates.test.ts has been updated to assert the presence of these new models in the registry and to ensure that gemini-2.0-flash remains the default model. There are no review comments, so I have no feedback to provide.

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[diegosouzapw]

Thanks @wilsonicdev! 🙌 This closes #3231 cleanly — refreshing the AI Studio static fallback so the provider tab shows current 3.x / 2.5 models on first run, while keeping gemini-2.0-flash as the default[0] ordering (the full catalog still comes from API sync once a key is added). The strengthened regression test asserting the new model IDs are present is a good guard. Verified the test locally (6/6 pass).

Merging into release/v3.8.11. Thanks for yet another tidy fix! 🚀