Move `public/*` to `public/assets/*`

Some old PRs (like #15219) introduced inconsistent directory system.

For example: why the local directory "public" is accessed by
`http://site/assets`? How to serve the ".well-known" files properly in
the public directory?

For convention rules, the "public" directory is widely used for the
website's root directory. It shouldn't be an exception for Gitea.

So, this PR makes the things consistent:

* `http://site/assets/foo` means `{CustomPath}/public/assets/foo`.
* `{CustomPath}/public/.well-known` and `{CustomPath}/public/robots.txt`
can be used in the future.

This PR is also a prerequisite for a clear solution for:
* #21942
* #25892 
* discourse.gitea.io: [.well-known path serving custom files behind
proxy?](https://discourse.gitea.io/t/well-known-path-serving-custom-files-behind-proxy/5445/1)

This PR is breaking for users who have custom "public" files (CSS/JS).
After getting approvals, I will update the documents.

----

## ⚠️ BREAKING ⚠️

If you have files in your "custom/public/" folder, please move them to
"custom/public/assets/".

---------

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: Giteabot <teabot@gitea.io>

Fixes https://github.com/go-gitea/gitea/issues/10410.
This PR removes around 120kB of CSS.

This was intended to be a small followup for
https://github.com/go-gitea/gitea/pull/23712, but...here we are.

1. Our docs currently use `slug` as the entire URL, which makes
refactoring tricky (see https://github.com/go-gitea/gitea/pull/23712).
Instead, this PR attempts to make future refactoring easier by using
slugs as an extension of the section. (Hugo terminology)
- What the above boils down to is this PR attempts to use directory
organization as URL management. e.g. `usage/comparison.en-us.md` ->
`en-us/usage/comparison/`, `usage/packages/overview.en-us.md` ->
`en-us/usage/packages/overview/`
- Technically we could even remove `slug`, as Hugo defaults to using
filename, however at least with this PR it means `slug` only needs to be
the name for the **current file** rather than an entire URL
2. This PR adds appropriate aliases (redirects) for pages, so anything
on the internet that links to our docs should hopefully not break.
3. A minor nit I've had for a while, renaming `seek-help` to `support`.
It's a minor thing, but `seek-help` has a strange connotation to it.
4. The commits are split such that you can review the first which is the
"actual" change, and the second is added redirects so that the first
doesn't break links elsewhere.

---------

Signed-off-by: jolheiser <john.olheiser@gmail.com>

For Docusaurus, it needs a meta data named `sidebar_position`, so we
copy all `weight` under `menu/sidebar` as top meta key.

- **Installation**: includes how to install Gitea and related other
tools, also includes upgrade Gitea
- **Administration**: includes how to configure Gitea, customize Gitea
and manage Gitea instance out of Gitea admin UI
- **Usage**: includes how to use Gitea's functionalities. A sub
documentation is about packages, in future we could also include CI/CD
and others.
- **Development**: includes how to integrate with Gitea's API, how to
develop new features within Gitea
- **Contributing**: includes how to contribute code to Gitea
repositories.

After this is merged, I think we can have a sub-documentation of `Usage`
part named `Actions` to describe how to use Gitea actions

---------

Co-authored-by: John Olheiser <john.olheiser@gmail.com>

* `git` -> `Git`
* `Github` and `github` -> `GitHub`
* `crowdin` -> `Crowdin`
* `git-lfs` -> `Git LFS`
* `githooks`, `git hooks`, `git-hooks` -> `Git Hooks`
* `discord` -> `Discord`
* `2fa` -> `2FA`
* `gitlab` and `Gitlab` -> `GitLab`
* `web hook` -> `webhook`
* `linux` -> `Linux`
* `sqlite` -> `SQLite`
* `MYSQL` and `mysql` -> `MySQL`
* rename refs to `master` branch -> `main`
* Fix English grammar

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: Lauris BH <lauris@nix.lv>

* Set background of openIDConnect logo to white in arc-green theme

* Fixed linting off arc-green theme

Signed-off-by: Leo Maroni <git@em0lar.de>

* Revert changes of first commit (white background) and replaced the image

* Updated openid_connect (part 2)

* Update public/img/auth/openid_connect.svg

Now in one line

Co-authored-by: silverwind <me@silverwind.io>

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: Lauris BH <lauris@nix.lv>

* draft

* Implement extract command

* Fix nits and force args on extract

* Add !bindata stub, support Windows, fmt

* fix vendored flag

* Remove leading slash for matching

* Add docs

* Fix typos

* Add embedded view command

Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>