Initial support for #25680
This PR only adds some simple styles from GitHub, it is big enough and
it focuses on adding the necessary framework-level supports. More styles
could be fine-tuned later.
Part of https://github.com/go-gitea/gitea/issues/27097:
- `gitea` theme is renamed to `gitea-light`
- `arc-green` theme is renamed to `gitea-dark`
- `auto` theme is renamed to `gitea-auto`
I put both themes in separate CSS files, removing all colors from the
base CSS. Existing users will be migrated to the new theme names. The
dark theme recolor will follow in a separate PR.
## ⚠️ BREAKING ⚠️
1. If there are existing custom themes with the names `gitea-light` or
`gitea-dark`, rename them before this upgrade and update the `theme`
column in the `user` table for each affected user.
2. The theme in `<html>` has moved from `class="theme-name"` to
`data-theme="name"`, existing customizations that depend on should be
updated.
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Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Giteabot <teabot@gitea.io>
This PR cleans up the docs in a way to make them simpler to ingest by
our [docs repo](https://gitea.com/gitea/gitea-docusaurus).
1. It includes all of the sed invocations our ingestion did, removing
the need to do it at build time.
2. It replaces the shortcode variable replacement method with
`@variable@` style, simply for easier sed invocations when required.
3. It removes unused files and moves the docs up a level as cleanup.
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Signed-off-by: jolheiser <john.olheiser@gmail.com>
