Options for other AI providers #4
Description
Currently, the extension requires users bring their own OpenAI key. One could imagine other providers being preferred by users, however.
This task is to set up some way for users to instead bring their own DeepSeek or Gemini key. There could be additional UI in options.html (and associated JS) such that the user could also indicate their preferred provider, or we could simply use an approach where the most recently entered API key is used.
DeepSeek and Gemini seem like the clearest two to build, but there could easily be others.