Reduce verbosity and positivity of Gemini code reviews

[deviantintegral]

https://github.com/Lullabot/drainpipe/pull/970#issuecomment-3391967293 is a great example of code review that is somehow more verbose yet less useful than just reading the code. It also uses superfluous language that overstates the impact of the PR such as "significantly enhances the reliability and user experience".

Let's follow the docs at https://developers.google.com/gemini-code-assist/docs/customize-gemini-behavior-github and improve this. In particular, code reviews should be:

• [ ] Terse
• [ ] Avoid unnecessary qualifiers
• [ ] Refrain from excessive positivity