fix(actions): correctness and hardening fixes (#38518)

Various fixes to actions

1. **Cap total jobs per run in reusable-workflow expansion** — only
nesting depth was capped, so fan-out + nested reusable workflows could
explode job-row inserts and exhaust the DB from a single push. Now
enforces `MaxJobNumPerRun` in the insert path.
2. **Reject rerun-failed when a run has no failed jobs** — an empty job
list meant "re-run everything", so `rerun-failed` on a green run re-ran
all jobs. Now errors (web + API).
3. **Don't adopt external commit statuses into the legacy hash** — the
pre-#35699 Context-only hash matched API-posted statuses too, collapsing
two same-named workflows into one check. Now limited to Actions-user
rows.
4. **Don't cut post-cancel cleanup short in `StopEndlessTasks`** — the
sweep force-stopped just-cancelled jobs mid-cleanup. Now targets
`StatusRunning` only; stalled cancels stay covered by `StopZombieTasks`.
5. **Avoid redundant run reload in `GenerateGiteaContext`** — resolving
`github.triggering_actor` reloaded the run already passed in. Now loads
only the trigger user via new `ActionRunAttempt.LoadTriggerUser`.

---------

Co-authored-by: Zettat123 <zettat123@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/api/v1/repo/action.go

@@ -1503,7 +1503,14 @@ func RerunFailedWorkflowRun(ctx *context.APIContext) {
 		return
 	}
 
-	if _, err := actions_service.RerunWorkflowRunJobs(ctx, ctx.Repo.Repository, run, ctx.Doer, actions_service.GetFailedJobsForRerun(jobs)); err != nil {
+	failedJobs := actions_service.GetFailedJobsForRerun(jobs)
+	// Empty failedJobs means no failed jobs to re-run
+	if len(failedJobs) == 0 {
+		ctx.APIError(http.StatusBadRequest, "this workflow run has no failed jobs to re-run")
+		return
+	}
+
+	if _, err := actions_service.RerunWorkflowRunJobs(ctx, ctx.Repo.Repository, run, ctx.Doer, failedJobs); err != nil {
 		handleWorkflowRerunError(ctx, err)
 		return
 	}