update !d from DDG to searx(ng); decide for instance (support !bangs)

since https://en.wikipedia.org/wiki/Searx supports bangs https://searxng.no-logs.com/info/en/search-syntax (! only)

we could move from DDG as default search engine to, maybe add one more layer of privacy?

https://searx.space/ lists public instances of searx, but it is hard to find an obvious choice to go for.

https://no-logs.com/:
```txt
- All analytics and nginx and user logs disabled.
- Up since 2023.
- Server located in 🇸🇪 Sweden.
```

Alternative could be to register a "few of them somehow", and "alternate between instances" for each search; a bit like a random round robin to distribute searches across searx instances (if that helps not sharing all searches in the same basket).

Start by reviewing the current DDG default-search and bang-handling entry point, then read the linked Searx/SearxNG search-syntax and instance information. The issue still needs a decision on one instance versus rotating instances; done would mean an agreed approach and corresponding default-search behavior.

Written by the indexing model from the issue text.