webui: add "6. Scenario" page — run scriptable test scenarios from removable media through the normal task queue

Exposes the scenario engine (platform.System.RunScenario, added earlier)
in the web UI instead of only the `bee run` CLI: a new nav item lists every
scenarios/*.json found on mounted removable media (GET /api/scenario/list)
and runs one with a click (POST /api/scenario/run), enqueued as a normal
Task with target "scenario" — progress/logs live in Tasks like any other
SAT pack, no separate live-output UI needed.

- app.go: satRunner gains RunScenario, exportManager gains
  ListScenarioFilesOnRemovableMedia/ReadScenarioFromRemovableMedia — both
  already implemented on platform.System, just newly exposed through App.
- webui/tasks.go: taskParams.ScenarioName; runTask's "scenario" case reads
  the file from removable media, parses it, and runs it.
- webui/page_scenario.go: the page itself.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

audit/internal/webui/api_test.go

@@ -46,6 +46,55 @@ func TestHandleAPISATRunDecodesBodyWithoutContentLength(t *testing.T) {
 	}
 }
 
+func TestHandleAPIScenarioRunRequiresName(t *testing.T) {
+	h := &handler{opts: HandlerOptions{App: &app.App{}}}
+	req := httptest.NewRequest("POST", "/api/scenario/run", strings.NewReader(`{}`))
+	rec := httptest.NewRecorder()
+
+	h.handleAPIScenarioRun(rec, req)
+
+	if rec.Code != 400 {
+		t.Fatalf("status=%d want 400, body=%s", rec.Code, rec.Body.String())
+	}
+}
+
+func TestHandleAPIScenarioRunEnqueuesTask(t *testing.T) {
+	globalQueue.mu.Lock()
+	originalTasks := globalQueue.tasks
+	globalQueue.tasks = nil
+	globalQueue.mu.Unlock()
+	t.Cleanup(func() {
+		globalQueue.mu.Lock()
+		globalQueue.tasks = originalTasks
+		globalQueue.mu.Unlock()
+	})
+
+	h := &handler{opts: HandlerOptions{App: &app.App{}}}
+	req := httptest.NewRequest("POST", "/api/scenario/run", strings.NewReader(`{"name":"power-watch"}`))
+	rec := httptest.NewRecorder()
+
+	h.handleAPIScenarioRun(rec, req)
+
+	if rec.Code != 200 {
+		t.Fatalf("status=%d body=%s", rec.Code, rec.Body.String())
+	}
+	globalQueue.mu.Lock()
+	defer globalQueue.mu.Unlock()
+	if len(globalQueue.tasks) != 1 {
+		t.Fatalf("tasks=%d want 1", len(globalQueue.tasks))
+	}
+	task := globalQueue.tasks[0]
+	if task.Target != "scenario" {
+		t.Fatalf("target=%q want scenario", task.Target)
+	}
+	if task.params.ScenarioName != "power-watch" {
+		t.Fatalf("scenario name=%q want power-watch", task.params.ScenarioName)
+	}
+	if task.Priority != taskPriorityBurn {
+		t.Fatalf("priority=%d want %d", task.Priority, taskPriorityBurn)
+	}
+}
+
 func TestHandleAPIBlackboxStatusReturnsDisabledWhenStateMissing(t *testing.T) {
 	h := &handler{opts: HandlerOptions{ExportDir: t.TempDir()}}
 	rec := httptest.NewRecorder()