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.

internal/handler/job_test.go

@@ -1,9 +1,7 @@
 package handler
 
 import (
-	"bytes"
 	"encoding/json"
-	"fmt"
 	"net/http"
 	"net/http/httptest"
 	"testing"
@@ -23,7 +21,7 @@ func setupJobRouter(h *JobHandler) *gin.Engine {
 	v1 := r.Group("/api/v1")
 	jobs := v1.Group("/jobs")
 	{
-		jobs.POST("/submit", h.SubmitJob)
+		// jobs.POST("/submit", h.SubmitJob) // [已弃用] 已被 POST /tasks 取代
 		jobs.GET("", h.GetJobs)
 		jobs.GET("/history", h.GetJobHistory)
 		jobs.GET("/:id", h.GetJob)
@@ -61,6 +59,8 @@ func handlerLogs(logs *observer.ObservedLogs) []observer.LoggedEntry {
 	return handler
 }
 
+// [已弃用] SubmitJob 相关测试已被禁用，该接口已被 POST /tasks 取代。
+/*
 func TestSubmitJob_Success(t *testing.T) {
 	mux := http.NewServeMux()
 	mux.HandleFunc("/slurm/v0.0.40/job/submit", func(w http.ResponseWriter, r *http.Request) {
@@ -171,6 +171,9 @@ func TestSubmitJob_SlurmError(t *testing.T) {
 		t.Fatalf("expected 502, got %d: %s", w.Code, w.Body.String())
 	}
 }
+*/
+
+// --- Logging verification tests ---
 
 func TestGetJobs_Success(t *testing.T) {
 	mux := http.NewServeMux()
@@ -462,6 +465,7 @@ func TestGetJobHistory_DefaultPagination(t *testing.T) {
 	}
 }
 
+/*
 func TestSubmitJob_InvalidBody(t *testing.T) {
 	mux := http.NewServeMux()
 	srv, handler := setupJobHandler(mux)
@@ -479,9 +483,11 @@ func TestSubmitJob_InvalidBody(t *testing.T) {
 		t.Fatalf("expected 400, got %d: %s", w.Code, w.Body.String())
 	}
 }
+*/
 
 // --- Logging verification tests ---
 
+/*
 func TestSubmitJob_InvalidBody_LogsWarn(t *testing.T) {
 	mux := http.NewServeMux()
 	srv, handler, logs := setupJobHandlerWithObserver(mux)
@@ -614,6 +620,7 @@ func TestSubmitJob_Success_NoHandlerLogs(t *testing.T) {
 		t.Errorf("expected no handler log entries on success, got %d", len(hLogs))
 	}
 }
+*/
 
 func TestGetJobs_Error_LogsError(t *testing.T) {
 	mux := http.NewServeMux()