add feature flag for gemini 3.5 flash

[shixiao-coder]

Gemini is planning to deprecate Gemini 3 flash preview in June 15th, this change is bumping up flash to 3.5, this change add feature flag for non prod to help bump up Gemini flash to 3.5

[gemini-code-assist]

Summary of Changes

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This pull request introduces a new feature flag to facilitate the upcoming migration from Gemini 3 Flash to Gemini 3.5 Flash. By adding this flag to the configuration files, the team can safely toggle and test the new model version across various environments in preparation for the scheduled deprecation of the previous version.

Highlights

• Feature Flag Addition: Added a new feature flag 'enable_gemini_3_5_flash' across all environment configurations to support the transition to Gemini 3.5 Flash.

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[gemini-code-assist]

Code Review

This pull request introduces a new feature flag, enable_gemini_3_5_flash, which is disabled by default across multiple environment configuration files (autopush, custom, dev, local, and staging). This flag is intended to enable Gemini 3.5 Flash for NL detection. There are no review comments, so I have no additional feedback to provide.