feat(snippets): add snippets entity, crud, and auto-browser-per-run

- add Snippet entity with name, description, code; full CRUD backend
- add snippets pages (list, create, edit, detail) and nav entry
- add runSnippet helper in code-executor using new Function with args array
- add result param to execute() so validateCode can access exec output
- remove sessionName from steps; each run now spawns its own fresh browser
- fix waitForURL race by polling localStorage for token instead

client/src/api/client.ts

@@ -10,6 +10,7 @@ import type {
   ScenarioRunDetail,
   ScenarioRunStep,
   ScenarioStep,
+  Snippet,
 } from './types';
 
 // In dev, Vite proxies /environments /sessions /scenarios /keys to localhost:3000.
@@ -58,6 +59,32 @@ export const credentials = {
   },
 };
 
+// ── Snippets ──────────────────────────────────────────────────────────────────
+
+export const snippets = {
+  list(page = 1, limit = 50): Promise<PaginatedResponse<Snippet>> {
+    return request(`/snippets?page=${page}&limit=${limit}`);
+  },
+  get(id: number): Promise<Snippet> {
+    return request(`/snippets/${id}`);
+  },
+  create(payload: Pick<Snippet, 'name' | 'code'> & { description?: string }): Promise<Snippet> {
+    return request('/snippets', {
+      method: 'POST',
+      body: JSON.stringify(payload),
+    });
+  },
+  update(id: number, patch: Partial<Pick<Snippet, 'name' | 'description' | 'code'>>): Promise<Snippet> {
+    return request(`/snippets/${id}`, {
+      method: 'PATCH',
+      body: JSON.stringify(patch),
+    });
+  },
+  remove(id: number): Promise<void> {
+    return request(`/snippets/${id}`, { method: 'DELETE' });
+  },
+};
+
 // ── Environments ──────────────────────────────────────────────────────────────
 
 export const environments = {
@@ -184,7 +211,6 @@ export interface CreateStepPayload {
   title?: string;
   order: number;
   type: 'login' | 'exec' | 'sign';
-  sessionName: string;
   execCode?: string;
   validateCode?: string;
 }
@@ -193,7 +219,6 @@ export interface UpdateStepPayload {
   title?: string;
   order?: number;
   type?: 'login' | 'exec' | 'sign';
-  sessionName?: string;
   execCode?: string;
   validateCode?: string;
 }

client/src/api/types.ts

@@ -35,6 +35,17 @@ export interface Credential {
   updatedAt: string;
 }
 
+// ── Snippets ──────────────────────────────────────────────────────────────────
+
+export interface Snippet {
+  id: number;
+  name: string;
+  description: string | null;
+  code: string;
+  createdAt: string;
+  updatedAt: string;
+}
+
 // ── Keys ──────────────────────────────────────────────────────────────────────
 
 export interface KeysResponse {
@@ -65,7 +76,7 @@ export interface ScenarioStep {
   order: number;
   type: StepType;
   title: string | null;
-  sessionName: string;
+  sessionName: string | null;
   execCode: string | null;
   validateCode: string | null;
   createdAt: string;