refactor(client): centralize error feedback with toast events

- emit API/network failures through a shared toast event bridge

- remove per-page inline error notifications to avoid duplicate error UI

- dedupe repeated toast messages to keep feedback readable

client/src/api/client.ts

@@ -11,19 +11,29 @@ import type {
   ScenarioStep,
   Snippet,
 } from './types';
+import { emitApiErrorToast } from '../lib/toast-events';
 
 // In dev, Vite proxies /environments /sessions /scenarios to localhost:3000.
 // In production (or when VITE_API_URL is set) we hit the configured origin directly.
 const BASE_URL: string = (import.meta.env.VITE_API_URL as string | undefined) ?? '';
 
 async function request<T>(path: string, init?: RequestInit): Promise<T> {
-  const res = await fetch(`${BASE_URL}${path}`, {
-    headers: { 'Content-Type': 'application/json', ...init?.headers },
-    ...init,
-  });
+  let res: Response;
+  try {
+    res = await fetch(`${BASE_URL}${path}`, {
+      headers: { 'Content-Type': 'application/json', ...init?.headers },
+      ...init,
+    });
+  } catch (err) {
+    const message = (err as Error).message || 'Network request failed';
+    emitApiErrorToast(message);
+    throw new Error(message);
+  }
   if (!res.ok) {
     const text = await res.text().catch(() => res.statusText);
-    throw new Error(`${res.status} ${text}`);
+    const message = `${res.status} ${text}`;
+    emitApiErrorToast(message);
+    throw new Error(message);
   }
   const contentLength = res.headers.get('content-length');
   if (res.status === 204 || contentLength === '0') return undefined as T;