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/README.md

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+# API Client
+
+This directory contains the auto-generated TypeScript API client for the STA backend.
+
+## Files
+
+- `schema.ts` - Auto-generated OpenAPI type definitions (do not edit manually)
+- `client.ts` - API client instance with type-safe methods
+
+## Regenerating the Client
+
+To regenerate the TypeScript client after backend API changes:
+
+1. Start the backend server:
+   ```bash
+   cargo run
+   ```
+
+2. Download the OpenAPI spec:
+   ```bash
+   curl http://localhost:3100/specs > openapi.yaml
+   ```
+
+3. Generate TypeScript types:
+   ```bash
+   pnpm exec openapi-typescript openapi.yaml -o src/api/schema.ts
+   ```
+
+## Usage Example
+
+```typescript
+import { apiClient } from '@/api/client';
+
+// GET request
+const { data, error } = await apiClient.GET('/api/health');
+if (error) {
+  console.error('Health check failed:', error);
+} else {
+  console.log('Server is healthy');
+}
+
+// GET request with response data
+const { data: meta, error: metaError } = await apiClient.GET('/api/meta');
+if (metaError) {
+  console.error('Failed to get metadata:', metaError);
+} else {
+  console.log('App name:', meta.name);
+  console.log('App version:', meta.version);
+}
+```
+
+## Configuration
+
+The API base URL can be configured via the `VITE_API_BASE_URL` environment variable.
+Create a `.env` file in the project root:
+
+```env
+VITE_API_BASE_URL=http://localhost:3100
+```
+
+For production builds, set the environment variable to point to your deployed backend.

src/api/client.ts

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+/**
+ * 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';

src/api/schema.ts

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+/**
+ * This file was auto-generated by openapi-typescript.
+ * Do not make direct changes to the file.
+ */
+
+export interface paths {
+    "/api/health": {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        get: {
+            parameters: {
+                query?: never;
+                header?: never;
+                path?: never;
+                cookie?: never;
+            };
+            requestBody?: never;
+            responses: {
+                /** @description Success */
+                200: {
+                    headers: {
+                        [name: string]: unknown;
+                    };
+                    content?: never;
+                };
+                /** @description Too Many Requests - rate limit exceeded */
+                429: {
+                    headers: {
+                        [name: string]: unknown;
+                    };
+                    content?: never;
+                };
+            };
+        };
+        put?: never;
+        post?: never;
+        delete?: never;
+        options?: never;
+        head?: never;
+        patch?: never;
+        trace?: never;
+    };
+    "/api/meta": {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        get: {
+            parameters: {
+                query?: never;
+                header?: never;
+                path?: never;
+                cookie?: never;
+            };
+            requestBody?: never;
+            responses: {
+                /** @description Success */
+                200: {
+                    headers: {
+                        [name: string]: unknown;
+                    };
+                    content: {
+                        "application/json; charset=utf-8": components["schemas"]["Meta"];
+                    };
+                };
+                /** @description Too Many Requests - rate limit exceeded */
+                429: {
+                    headers: {
+                        [name: string]: unknown;
+                    };
+                    content?: never;
+                };
+            };
+        };
+        put?: never;
+        post?: never;
+        delete?: never;
+        options?: never;
+        head?: never;
+        patch?: never;
+        trace?: never;
+    };
+}
+export type webhooks = Record<string, never>;
+export interface components {
+    schemas: {
+        /** Meta */
+        Meta: {
+            version: string;
+            name: string;
+        };
+    };
+    responses: never;
+    parameters: never;
+    requestBodies: never;
+    headers: never;
+    pathItems: never;
+}
+export type $defs = Record<string, never>;
+export type operations = Record<string, never>;