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/user/settings/organization.tmpl

@@ -23,9 +23,9 @@
 								</button>
 							</form>
 						</div>
-						{{avatar $.Context . 28 "mini"}}
-						<div class="content">
-								<a href="{{.HomeLink}}">{{.Name}}</a>
+						<div class="content gt-df gt-ac gt-gap-3">
+							{{avatar $.Context . 28 "mini"}}
+							<a class="muted" href="{{.HomeLink}}">{{.Name}}</a>
 						</div>
 					</div>
 					{{end}}