Closes#7434
Replaces the `PREVIEW` selector (removed in #7389) with a configuration
option `explicit-preview-rules` which requires selectors to use exact
rule codes for all preview rules. This allows users to enable preview
without opting into all preview rules at once.
## Test plan
Unit tests
## Summary
We're planning to move the documentation from
[https://beta.ruff.rs/docs](https://beta.ruff.rs/docs) to
[https://docs.astral.sh/ruff](https://docs.astral.sh/ruff), for a few
reasons:
1. We want to remove the `beta` from the domain, as Ruff is no longer
considered beta software.
2. We want to migrate to a structure that could accommodate multiple
future tools living under one domain.
The docs are actually already live at
[https://docs.astral.sh/ruff](https://docs.astral.sh/ruff), but later
today, I'll add a permanent redirect from the previous to the new
domain. **All existing links will continue to work, now and in
perpetuity.**
This PR contains the code changes necessary for the updated
documentation. As part of this effort, I moved the playground and
documentation from my personal Cloudflare account to our team Cloudflare
account (hence the new `--project-name` references). After merging, I'll
also update the secrets on this repo.
