Various UI fixes (#25264)

Numerous small UI fixes:

- Fix double border in collaborator list
- Fix system notice table background
- Mute links in repo and org lists
- Downsize projects edit buttons
- Improve milestones and project list rendering
- Condense milestone list entry to a single line of "metas"
- Mute ".." button in repo files list

templates/admin/notice.tmpl

@@ -3,7 +3,7 @@
 		<h4 class="ui top attached header">
 			{{.locale.Tr "admin.notices.system_notice_list"}} ({{.locale.Tr "admin.total" .Total}})
 		</h4>
-		<table class="ui attached basic select selectable table unstackable g-table-auto-ellipsis">
+		<table class="ui attached segment select selectable striped table unstackable g-table-auto-ellipsis">
 			<thead>
 				<tr>
 					<th></th>