fix(task): prevent duplicate Slurm job submission on backend restart

RecoverStuckTasks now skips tasks that already have a slurm_job_id,
and ProcessTask adds a guard before the submitting step to prevent
re-submission even if a task is incorrectly re-enqueued.

Also deprecates POST /api/v1/jobs/submit endpoint (replaced by POST /tasks)
and comments out related handlers and tests.

cmd/server/integration_job_test.go

@@ -3,7 +3,6 @@ package main
 import (
 	"bytes"
 	"encoding/json"
-	"fmt"
 	"net/http"
 	"testing"
 
@@ -66,6 +65,8 @@ func jobSubmitViaAPI(t *testing.T, env *testenv.TestEnv, script string) int32 {
 	return job.JobID
 }
 
+// [已弃用] 以下测试依赖 POST /api/v1/jobs/submit，该接口已被 POST /tasks 取代。
+/*
 // TestIntegration_Jobs_Submit verifies POST /api/v1/jobs/submit creates a new job.
 func TestIntegration_Jobs_Submit(t *testing.T) {
 	env := testenv.NewTestEnv(t)
@@ -220,3 +221,4 @@ func TestIntegration_Jobs_History(t *testing.T) {
 		t.Fatalf("cancelled job %d not found in history", jobID)
 	}
 }
+*/