Clean up various avatar dimensions (#24701)

Clean up a few cases where avatar dimensions were overwritten via CSS,
which were no longer needed or were possible to set via HTML width.

Also included are two small fixes:

- Fix one more case of incorrect avatar offset on review timeline
- Vertically center avatars in review sidebar

There is more to be done here, but some of the work depends on Fomantic
`comment` module removal, or in the case of org member lists, a refactor
of the `avatarlink` template to accept a size.

<img width="371" alt="image"
src="https://github.com/go-gitea/gitea/assets/115237/9c5902fb-2b89-4a7d-a152-60e74c3b2c56">
<img width="306" alt="image"
src="https://github.com/go-gitea/gitea/assets/115237/c8d92e2a-91c9-4f4a-a7de-6ae1a6bc0479">

---------

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

templates/repo/issue/view_content.tmpl

@@ -11,10 +11,12 @@
 		<div class="ui timeline">
 			<div id="{{.Issue.HashTag}}" class="timeline-item comment first">
 				{{if .Issue.OriginalAuthor}}
-				<span class="timeline-avatar"><img src="{{AppSubUrl}}/assets/img/avatar_default.png"></span>
+				<span class="timeline-avatar">
+					<img src="{{AppSubUrl}}/assets/img/avatar_default.png" width="40" height="40">
+				</span>
 				{{else}}
 				<a class="timeline-avatar" {{if gt .Issue.Poster.ID 0}}href="{{.Issue.Poster.HomeLink}}"{{end}}>
-					{{avatar $.Context .Issue.Poster}}
+					{{avatar $.Context .Issue.Poster 40}}
 				</a>
 				{{end}}
 				<div class="content comment-container">
@@ -33,7 +35,7 @@
 								</span>
 							{{else}}
 								<a class="inline-timeline-avatar" href="{{.Issue.Poster.HomeLink}}">
-									{{avatar $.Context .Issue.Poster}}
+									{{avatar $.Context .Issue.Poster 24}}
 								</a>
 								<span class="text grey">
 									{{template "shared/user/authorlink" .Issue.Poster}}
@@ -93,7 +95,7 @@
 				{{if and (or .IsRepoAdmin .HasIssuesOrPullsWritePermission (not .Issue.IsLocked)) (not .Repository.IsArchived)}}
 				<div class="timeline-item comment form">
 					<a class="timeline-avatar" href="{{.SignedUser.HomeLink}}">
-						{{avatar $.Context .SignedUser}}
+						{{avatar $.Context .SignedUser 40}}
 					</a>
 					<div class="content">
 						<form class="ui segment form" id="comment-form" action="{{$.RepoLink}}/issues/{{.Issue.Index}}/comments" method="post">