fix: use context.Background() in TriggerRun so job outlives HTTP request

r.Context() is cancelled when the HTTP handler returns (after 201 is sent),
causing the job to be immediately marked as cancelled_shutdown before WoL
even runs. Use context.Background() so the job goroutine runs independently
of the HTTP request lifecycle.

internal/api/handlers_jobs.go

@@ -1,6 +1,7 @@
 package api
 
 import (
+	"context"
 	"database/sql"
 	"encoding/json"
 	"fmt"
@@ -160,7 +161,7 @@ func (h *JobHandler) TriggerRun(w http.ResponseWriter, r *http.Request) {
 				slog.Error("job run goroutine panicked", "job_id", jobID, "panic", r)
 			}
 		}()
-		h.engine.Run(r.Context(), jobID, pairID)
+		h.engine.Run(context.Background(), jobID, pairID)
 	}()
 
 	jobRepo := models.NewJobRepository(h.db)