Support Gemini 3.1 and 3.5 Flash for Google Vertex AI Provider

Problem

Currently, the Google Vertex AI provider in BoltAI is missing recent models, such as the Gemini 3.1 series (including 3.1 Pro Preview) and Gemini 3.5 Flash. Additionally, other non-Gemini models offered through Vertex AI are not supported. Because the AI models evolves rapidly, it is difficult to maintain and update a hardcoded list every time a new model is released.

Proposed Solution

Add Gemini 3.1 Pro and 3.5 Flash next release for a quick fix. For the long run, add a custom "Model ID" input field within the Google Vertex AI provider settings. This would allow users to manually enter the exact ID of the language model they wish to use.

Benefits

This approach future-proofs the integration. Instead of waiting for Daniel to release an update with a new model, users can instantly access the latest models (like Gemini 3.1 Pro Preview and 3.5 Flash) or any other supported Vertex AI model simply by entering the corresponding model ID.