Fixes https://github.com/go-gitea/gitea/issues/30005. Regression from
https://github.com/go-gitea/gitea/pull/29945.
There was only once instance of `tw-content-center` before that PR, so I
just ran below command and reverted that one instance.
```sh
perl -p -i -e 's#tw-content-center#tw-items-center#g' web_src/js/**/* templates/**/* models/**/* tests/**/*
```
(cherry picked from commit 04f9ad056882fc3f21b247b16f84437adf0f36d8)
Conflicts:
templates/repo/diff/conversation.tmpl
templates/repo/header.tmpl
templates/repo/issue/filter_list.tmpl
templates/repo/issue/view_content/conversation.tmpl
templates/repo/wiki/view.tmpl
web_src/js/components/DashboardRepoList.vue
re-ran the command after discarding the Gitea changes to
ensure all Forgejo files are also covered
Unify all but a few search boxes to use uniform style, uniform
translations and shared templates where possible.
Remove a few duplicated search templates, e. g. code search.
<details><summary>Example after screenshots:</summary>




</details>
Also includes #29700
Co-authored-by: 6543 <6543@obermui.de>
---------
Co-authored-by: 6543 <m.huber@kithara.com>
Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Giteabot <teabot@gitea.io>
Conflicts:
routers/web/repo/search.go
templates/repo/home.tmpl
templates/repo/search.tmpl
templates/shared/repo_search.tmpl
Filter Repositories by type (resolves#1170, #1318)
before:

after:

(cherry picked from commit e3524c63d6d42865ea8288af89b372544d35474b)