Follow-up to #37987, addressing the unresolved review comments on the
org members search form.
And fix more trivial problems together (see the commit titles)
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Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
1. Fix the "flash message" layout problem for different cases
* I am sure most of the users should have ever seen the ugly
center-aligned error message with multiple lines.
2. Fix inconsistent "Details" flash message EOL handling, sometimes
`\n`, sometimes `<br>`
* Now, always use "\n" and use `<pre>` to render
3. Remove SanitizeHTML template func because it is not useful and can be
easily abused.
* But it is still kept for mail templates, for example:
https://github.com/go-gitea/gitea/issues/36049
4. Clarify PostProcessCommitMessage's behavior and add FIXME comment
By the way: cleaned up some devtest pages, move embedded style block to
CSS file