Expose content_version for optimistic locking on issue and PR edits (#37035)

- Add `content_version` field to Issue and PullRequest API responses
- Accept optional `content_version` in `PATCH
/repos/{owner}/{repo}/issues/{index}` and `PATCH
/repos/{owner}/{repo}/pulls/{index}` — returns 409 Conflict when stale,
succeeds silently when omitted (backward compatible)
- Pre-check `content_version` before any mutations to prevent partial
writes (e.g. title updated but body rejected)

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

services/convert/issue.go

@@ -62,7 +62,8 @@ func toIssue(ctx context.Context, doer *user_model.User, issue *issues_model.Iss
 		Updated:     issue.UpdatedUnix.AsTime(),
 		PinOrder:    util.Iif(issue.PinOrder == -1, 0, issue.PinOrder), // -1 means loaded with no pin order
 
-		TimeEstimate: issue.TimeEstimate,
+		TimeEstimate:   issue.TimeEstimate,
+		ContentVersion: issue.ContentVersion,
 	}
 
 	if issue.Repo != nil {

services/convert/pull.go

@@ -97,6 +97,7 @@ func ToAPIPullRequest(ctx context.Context, pr *issues_model.PullRequest, doer *u
 		Created:        pr.Issue.CreatedUnix.AsTimePtr(),
 		Updated:        pr.Issue.UpdatedUnix.AsTimePtr(),
 		PinOrder:       util.Iif(apiIssue.PinOrder == -1, 0, apiIssue.PinOrder),
+		ContentVersion: apiIssue.ContentVersion,
 
 		// output "[]" rather than null to align to github outputs
 		RequestedReviewers:      []*api.User{},
@@ -372,6 +373,7 @@ func ToAPIPullRequests(ctx context.Context, baseRepo *repo_model.Repository, prs
 			Created:        pr.Issue.CreatedUnix.AsTimePtr(),
 			Updated:        pr.Issue.UpdatedUnix.AsTimePtr(),
 			PinOrder:       util.Iif(apiIssue.PinOrder == -1, 0, apiIssue.PinOrder),
+			ContentVersion: apiIssue.ContentVersion,
 
 			AllowMaintainerEdit: pr.AllowMaintainerEdit,