feat: add stable versions of Gemini 3/3.1 and Qwen 3.5-flash models

[archer-claw]

What does this PR do?

Adds missing model configurations to FastGPT Plugin based on current provider documentation.

• Gemini: Added gemini-3.1-pro and gemini-3-flash stable models to accompany the existing previews.
• Qwen (AliCloud): Added the lightweight qwen3.5-flash model. Note: As per request, the 'omni' series was excluded from this update.

This ensures FastGPT stays current with the latest stable model releases.

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[cla-assistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

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[github-actions]

✅ Build Successful - Preview Images for this PR:

registry.cn-hangzhou.aliyuncs.com/fastgpt/fastgpt-plugin-pr:92eb97c8c0f292cbcf5a6236de31ac414210409a

Changed packages:
None