fix(webui): dispatch "scenario" tasks in the real task runner, collapse duplicate target switch

The Scenario page's Run button enqueued a task with target "scenario" that
never launched any load: the queue runs each task in an external
bee-worker subprocess (RunPersistedTask -> executeTaskWithOptions in
task_runner.go), whose target switch had no "scenario" case, so the task
died with "unknown target: scenario". The case had only been added to
taskQueue.runTask's switch in tasks.go — a stale copy exercised solely by
unit tests, which is why the tests passed while the button did nothing.

Add the "scenario" case (ReadScenario -> ParseScenarioJSON -> RunScenario)
to executeTaskWithOptions, and collapse runTask into a thin delegate to it
so there is a single target dispatch. The old runTask switch had already
drifted into a subset (missing nvme-format, *-write, raid-*, nvidia-config,
...); removing it eliminates the divergence that hid this bug. Also drop the
now-orphaned taskQueue.statusDB helper.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

audit/internal/webui/task_runner.go

@@ -231,6 +231,22 @@ func executeTaskWithOptions(opts *HandlerOptions, t *Task, j *jobState, ctx cont
 			break
 		}
 		archive, err = a.RunNCCLTests(ctx, "", t.params.GPUIndices, j.append)
+	case "scenario":
+		if a == nil {
+			err = fmt.Errorf("app not configured")
+			break
+		}
+		var data []byte
+		data, err = a.ReadScenario(t.params.ScenarioName)
+		if err != nil {
+			break
+		}
+		var spec platform.ScenarioSpec
+		spec, err = platform.ParseScenarioJSON(data)
+		if err != nil {
+			break
+		}
+		archive, err = a.RunScenario(ctx, "", spec, j.append)
 	case "nvidia-stress":
 		if a == nil {
 			err = fmt.Errorf("app not configured")