feat(discover): update searxng query options to include categories and time range

[Davixk]

hardcoding to a predefined engine doesn't allow any customization.

by using categories rather than preset engines, the SearXNG deployment now has the freedom to use its internal engines setup, allowing for much more freedom.

also, setting a time_range of one month ensures retrieved articles are not stale, and the news will be more up to date.

[ItzCrazyKns]

Thanks for the PR. You're right that using categories gives more flexibility in terms of engine setup and time filtering.

That said, I have plans to add user specific customization to the /discover route in the near future, where users can indicate the topics they're interested in. Currently, we hardcode the sources to ensure consistent article quality and relevance, since switching to broader news categories can sometimes introduce lower quality or off topic content (e.g. clickbait, outdated coverage, or SEO spam depending on the engine mix) - I have tested it.

If you’d like to keep just the time_range change and drop the rest for now, I’d love to merge this