Remove .segment from .project-column (#31204)

Using `.segment` on the project columns is a major abuse of that class,
so remove it and instead set the border-radius directly on it.

Fixes: https://github.com/go-gitea/gitea/issues/31129

templates/projects/view.tmpl

@@ -66,7 +66,7 @@
 <div id="project-board">
 	<div class="board {{if .CanWriteProjects}}sortable{{end}}"{{if .CanWriteProjects}} data-url="{{$.Link}}/move"{{end}}>
 		{{range .Columns}}
-			<div class="ui segment project-column"{{if .Color}} style="background: {{.Color}} !important; color: {{ContrastColor .Color}} !important"{{end}} data-id="{{.ID}}" data-sorting="{{.Sorting}}" data-url="{{$.Link}}/{{.ID}}">
+			<div class="project-column"{{if .Color}} style="background: {{.Color}} !important; color: {{ContrastColor .Color}} !important"{{end}} data-id="{{.ID}}" data-sorting="{{.Sorting}}" data-url="{{$.Link}}/{{.ID}}">
 				<div class="project-column-header{{if $canWriteProject}} tw-cursor-grab{{end}}">
 					<div class="ui circular label project-column-issue-count">
 						{{.NumIssues ctx}}

web_src/css/features/projects.css

@@ -9,6 +9,7 @@
 .project-column {
   background-color: var(--color-project-column-bg) !important;
   border: 1px solid var(--color-secondary) !important;
+  border-radius: var(--border-radius);
   margin: 0 0.5rem !important;
   padding: 0.5rem !important;
   width: 320px;