feat(api): generate TypeScript API client from OpenAPI specification

Create type-safe TypeScript API client automatically generated from the
OpenAPI specification. Includes generated schema types and documented client
wrapper for type-safe backend communication.

Ref: T008 (specs/001-modbus-relay-control)

src/api/client.ts

@@ -0,0 +1,31 @@
+/**
+ * API client for the STA backend.
+ *
+ * This client is generated from the OpenAPI specification and provides
+ * type-safe access to all backend endpoints.
+ *
+ * Usage:
+ * ```typescript
+ * import { apiClient } from '@/api/client';
+ *
+ * const { data, error } = await apiClient.GET('/api/health');
+ * ```
+ */
+
+import createClient from 'openapi-fetch';
+import type { paths } from './schema';
+
+// Get the API base URL from environment variables or default to localhost
+const API_BASE_URL = import.meta.env.VITE_API_BASE_URL || 'http://localhost:3100';
+
+/**
+ * Typed API client instance.
+ *
+ * All requests are type-checked against the OpenAPI schema.
+ */
+export const apiClient = createClient<paths>({ baseUrl: API_BASE_URL });
+
+/**
+ * Re-export the types for convenience
+ */
+export type { paths, components } from './schema';