Simplify review UI (#31062)

Instead of always displaying all available actions as buttons, merge
them into a single dropdown menu, same as GitHub. That decreases visual
overload and is more mobile-friendly, while not losing any
functionality.

## Screenshots
<details><summary>Before</summary>

![grafik](https://github.com/go-gitea/gitea/assets/51889757/b957fab0-4cc7-4cf5-a6c8-33f571be7b19)
</details> 
<details><summary>After (unexpanded)</summary>


![grafik](https://github.com/go-gitea/gitea/assets/51889757/c8fd3428-4092-4295-bd55-c243409ba90d)
</details>
 
<details><summary>After (expanded)</summary>

![grafik](https://github.com/go-gitea/gitea/assets/51889757/c0eada91-54be-42ce-9db1-0db56d971438)
</details>

templates/repo/diff/box.tmpl

@@ -159,26 +159,31 @@
 								{{if and $isReviewFile $file.HasChangedSinceLastReview}}
 									<span class="changed-since-last-review unselectable not-mobile">{{ctx.Locale.Tr "repo.pulls.has_changed_since_last_review"}}</span>
 								{{end}}
+								{{if $isReviewFile}}
+									<label data-link="{{$.Issue.Link}}/viewed-files" data-headcommit="{{$.AfterCommitID}}" class="viewed-file-form unselectable{{if $file.IsViewed}} viewed-file-checked-form{{end}}">
+										<input type="checkbox" name="{{$file.GetDiffFileName}}" autocomplete="off"{{if $file.IsViewed}} checked{{end}}> {{ctx.Locale.Tr "repo.pulls.has_viewed_file"}}
+									</label>
+								{{end}}
+								<div class="ui dropdown basic">
+									{{svg "octicon-kebab-horizontal" 18 "icon tw-mx-2"}}
+									<div class="ui menu">
 										{{if not (or $file.IsIncomplete $file.IsBin $file.IsSubmodule)}}
-									<button class="ui basic tiny button unescape-button not-mobile">{{ctx.Locale.Tr "repo.unescape_control_characters"}}</button>
-									<button class="ui basic tiny button escape-button tw-hidden">{{ctx.Locale.Tr "repo.escape_control_characters"}}</button>
+											<button class="unescape-button item">{{ctx.Locale.Tr "repo.unescape_control_characters"}}</button>
+											<button class="escape-button tw-hidden item">{{ctx.Locale.Tr "repo.escape_control_characters"}}</button>
 										{{end}}
 										{{if and (not $file.IsSubmodule) (not $.PageIsWiki)}}
 											{{if $file.IsDeleted}}
-										<a class="ui basic tiny button" rel="nofollow" href="{{$.BeforeSourcePath}}/{{PathEscapeSegments .Name}}">{{ctx.Locale.Tr "repo.diff.view_file"}}</a>
+												<a class="item" rel="nofollow" href="{{$.BeforeSourcePath}}/{{PathEscapeSegments .Name}}">{{ctx.Locale.Tr "repo.diff.view_file"}}</a>
 											{{else}}
-										<a class="ui basic tiny button" rel="nofollow" href="{{$.SourcePath}}/{{PathEscapeSegments .Name}}">{{ctx.Locale.Tr "repo.diff.view_file"}}</a>
+												<a class="item" rel="nofollow" href="{{$.SourcePath}}/{{PathEscapeSegments .Name}}">{{ctx.Locale.Tr "repo.diff.view_file"}}</a>
 												{{if and $.Repository.CanEnableEditor $.CanEditFile (not $file.IsLFSFile) (not $file.IsBin)}}
-											<a class="ui basic tiny button" rel="nofollow" href="{{$.HeadRepoLink}}/_edit/{{PathEscapeSegments $.HeadBranchName}}/{{PathEscapeSegments $file.Name}}?return_uri={{print $.BackToLink "#diff-" $file.NameHash | QueryEscape}}">{{ctx.Locale.Tr "repo.editor.edit_this_file"}}</a>
-										{{end}}
+													<a class="item" rel="nofollow" href="{{$.HeadRepoLink}}/_edit/{{PathEscapeSegments $.HeadBranchName}}/{{PathEscapeSegments $file.Name}}?return_uri={{print $.BackToLink "#diff-" $file.NameHash | QueryEscape}}">{{ctx.Locale.Tr "repo.editor.edit_this_file"}}</a>
 												{{end}}
 											{{end}}
-								{{if $isReviewFile}}
-									<label data-link="{{$.Issue.Link}}/viewed-files" data-headcommit="{{$.AfterCommitID}}" class="viewed-file-form unselectable{{if $file.IsViewed}} viewed-file-checked-form{{end}}">
-										<input type="checkbox" name="{{$file.GetDiffFileName}}" autocomplete="off"{{if $file.IsViewed}} checked{{end}}> {{ctx.Locale.Tr "repo.pulls.has_viewed_file"}}
-									</label>
 										{{end}}
 									</div>
+								</div>
+							</div>
 						</h4>
 						<div class="diff-file-body ui attached unstackable table segment" {{if and $file.IsViewed $.IsShowingAllCommits}}data-folded="true"{{end}}>
 							<div id="diff-source-{{$file.NameHash}}" class="file-body file-code unicode-escaped code-diff{{if $.IsSplitStyle}} code-diff-split{{else}} code-diff-unified{{end}}{{if $showFileViewToggle}} tw-hidden{{end}}">