refactor(client): group pages by entity and add scenario/step crud

- move environment, scenario, session pages into entity subdirs
- add CreateScenarioPage and EditScenarioPage
- add CreateStepPage and EditStepPage with order/type/session/code fields
- add per-step edit and delete row actions on ScenarioDetailPage
- add step api methods (get, create, update, remove) to api client
- add sectionToolbar, formField, fieldLabel, textarea css utilities

client/src/api/client.ts

@@ -113,3 +113,42 @@ export const scenarios = {
     return request(`/scenarios/${scenarioId}/runs?page=${page}&limit=${limit}`);
   },
 };
+
+// ── Scenario Steps ────────────────────────────────────────────────────────────
+
+export interface CreateStepPayload {
+  order: number;
+  type: 'login' | 'exec' | 'sign';
+  sessionName: string;
+  execCode?: string;
+  validateCode?: string;
+}
+
+export interface UpdateStepPayload {
+  order?: number;
+  type?: 'login' | 'exec' | 'sign';
+  sessionName?: string;
+  execCode?: string;
+  validateCode?: string;
+}
+
+export const steps = {
+  get(scenarioId: number, stepId: number): Promise<ScenarioStep> {
+    return request(`/scenarios/${scenarioId}/steps/${stepId}`);
+  },
+  create(scenarioId: number, payload: CreateStepPayload): Promise<ScenarioStep> {
+    return request(`/scenarios/${scenarioId}/steps`, {
+      method: 'POST',
+      body: JSON.stringify(payload),
+    });
+  },
+  update(scenarioId: number, stepId: number, payload: UpdateStepPayload): Promise<ScenarioStep> {
+    return request(`/scenarios/${scenarioId}/steps/${stepId}`, {
+      method: 'PATCH',
+      body: JSON.stringify(payload),
+    });
+  },
+  remove(scenarioId: number, stepId: number): Promise<void> {
+    return request(`/scenarios/${scenarioId}/steps/${stepId}`, { method: 'DELETE' });
+  },
+};