feat(api): add last_sync to repository API (#37566)

This PR adds a new repository API field, `mirror_last_sync_at`, to
expose the timestamp of the last successful pull mirror sync.

Unlike `mirror_updated`, this field does not affect mirror scheduling
and is updated only after a successful pull sync. Failed sync attempts
leave the value unchanged.

What changed

- added `mirror_last_sync_at` to the repository API response
- updated pull mirror sync flow to persist the timestamp only on
successful sync
- kept `mirror_updated` behavior unchanged for queue/scheduling purposes

`mirror_updated` is currently tied to mirror queue behavior, so it
cannot safely represent the last successful sync time. The new field
makes that state explicit for API consumers without changing scheduling
semantics.

---------

Signed-off-by: pomidorry <106489913+Pomidorry@users.noreply.github.com>
Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Giteabot <teabot@gitea.io>

services/convert/repository.go

@@ -152,11 +152,13 @@ func innerToRepo(ctx context.Context, repo *repo_model.Repository, permissionInR
 
 	mirrorInterval := ""
 	var mirrorUpdated time.Time
+	var lastSync time.Time
 	if repo.IsMirror {
 		pullMirror, err := repo_model.GetMirrorByRepoID(ctx, repo.ID)
 		if err == nil {
 			mirrorInterval = pullMirror.Interval.String()
 			mirrorUpdated = pullMirror.UpdatedUnix.AsTime()
+			lastSync = pullMirror.LastSyncUnix.AsTime()
 		}
 	}
 
@@ -247,6 +249,7 @@ func innerToRepo(ctx context.Context, repo *repo_model.Repository, permissionInR
 		DefaultTargetBranch:           defaultTargetBranch,
 		AvatarURL:                     repo.AvatarLink(ctx),
 		Internal:                      !repo.IsPrivate && repo.Owner.Visibility == api.VisibleTypePrivate,
+		MirrorLastSyncAt:              lastSync,
 		MirrorInterval:                mirrorInterval,
 		MirrorUpdated:                 mirrorUpdated,
 		RepoTransfer:                  transfer,

services/mirror/mirror_pull.go

@@ -305,6 +305,7 @@ func SyncPullMirror(ctx context.Context, repoID int64) bool {
 
 	log.Trace("SyncMirrors [repo: %-v]: Scheduling next update", m.Repo)
 	m.ScheduleNextUpdate()
+	m.LastSyncUnix = m.UpdatedUnix
 	if err = repo_model.UpdateMirror(ctx, m); err != nil {
 		log.Error("SyncMirrors [repo: %-v]: failed to UpdateMirror with next update date: %v", m.Repo, err)
 		return false