Refactor "flex-list" to "flex-divided-list" (#37505)

Purpose:

1. Make the whole code base have unified "item" layout
2. Clarify our "list" styles: "flex-relaxed-list", "flex-divided-list"
3. Prepare to replace legacy "ui relaxed list"
* https://github.com/go-gitea/gitea/pull/37445#discussion_r3144458865
4. Prepare for refactoring the "pull merge box", it needs the
"flex-divided-list"
    * related to "Refactor pull request view (*)" like #37451
5. Fix legacy abuses of "flex-list", e.g.: repo home sidebar

tests/e2e/issue-project.test.ts

@@ -335,7 +335,7 @@ test('filter issues with no project using project=-1', async ({page}) => {
     await expect(page.locator('#issue-list')).not.toContainText('Issue with project assigned');
 
     // Verify the last item in the list is NOT the issue with a project
-    const issueItems = page.locator('#issue-list .flex-item');
+    const issueItems = page.locator('#issue-list .item');
     const lastIssueItem = issueItems.last();
     await expect(lastIssueItem).not.toContainText('Issue with project assigned');
   } finally {

tests/integration/auth_ldap_test.go

@@ -395,7 +395,7 @@ func testLDAPUserSyncSSHKeys(t *testing.T) {
 		resp := session.MakeRequest(t, req, http.StatusOK)
 		htmlDoc := NewHTMLParser(t, resp.Body)
 
-		divs := htmlDoc.doc.Find("#keys-ssh .flex-item .flex-item-body:not(:last-child)")
+		divs := htmlDoc.doc.Find("#keys-ssh .item .item-body:not(:last-child)")
 		syncedKeys := make([]string, divs.Length())
 		for i := 0; i < divs.Length(); i++ {
 			syncedKeys[i] = strings.TrimSpace(divs.Eq(i).Text())

tests/integration/issue_test.go

@@ -34,7 +34,7 @@ import (
 func getIssuesSelection(t testing.TB, htmlDoc *HTMLDoc) *goquery.Selection {
 	issueList := htmlDoc.doc.Find("#issue-list")
 	assert.Equal(t, 1, issueList.Length())
-	return issueList.Find(".flex-item").Find(".issue-title")
+	return issueList.Find(".item").Find(".issue-title")
 }
 
 func getIssue(t *testing.T, repoID int64, issueSelection *goquery.Selection) *issues_model.Issue {

tests/integration/privateactivity_test.go

@@ -57,7 +57,7 @@ func testPrivateActivityHelperEnablePrivateActivity(t *testing.T) {
 }
 
 func testPrivateActivityHelperHasVisibleActivitiesInHTMLDoc(htmlDoc *HTMLDoc) bool {
-	return htmlDoc.doc.Find("#activity-feed").Find(".flex-item").Length() > 0
+	return htmlDoc.doc.Find("#activity-feed").Find(".item").Length() > 0
 }
 
 func testPrivateActivityHelperHasVisibleActivitiesFromSession(t *testing.T, session *TestSession) bool {

tests/integration/repo_fork_test.go

@@ -82,7 +82,7 @@ func TestRepoForkToOrg(t *testing.T) {
 
 func TestForkListLimitedAndPrivateRepos(t *testing.T) {
 	defer tests.PrepareTestEnv(t)()
-	forkItemSelector := ".fork-list .flex-item"
+	forkItemSelector := ".fork-list .item"
 
 	user1Sess := loginUser(t, "user1")
 	user1 := unittest.AssertExistsAndLoadBean(t, &user_model.User{Name: "user1"})