feat(desktop): add API client with auth headers

Add fetch wrapper for desktop renderer to call Multica backend REST API.
Attaches sid, device-id, and os-type headers automatically using
useAuthStore and electronAPI.auth.getDeviceIdHeader().

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/desktop/src/renderer/src/service/request.ts

@@ -0,0 +1,72 @@
+import { useAuthStore } from '../stores/auth'
+
+// Backend API host — change this when switching environments
+const API_HOST = 'https://api-dev.copilothub.ai'
+
+/**
+ * Fetch request wrapper for desktop app.
+ * Attaches sid, device-id, and os-type headers automatically.
+ */
+export async function request<T = unknown>(url: string, options: RequestInit = {}): Promise<T> {
+  const sid = useAuthStore.getState().sid
+  const deviceIdHeader = await window.electronAPI.auth.getDeviceIdHeader()
+
+  const config: RequestInit = {
+    ...options,
+    headers: {
+      'Content-Type': 'application/json',
+      'os-type': '3',
+      ...(deviceIdHeader && { 'device-id': deviceIdHeader }),
+      ...(sid && { sid }),
+      ...options.headers,
+    },
+  }
+
+  const response = await fetch(`${API_HOST}${url}`, config)
+
+  let data: T
+  const contentType = response.headers.get('content-type')
+  if (contentType?.includes('application/json')) {
+    data = await response.json()
+  } else {
+    const text = await response.text()
+    data = { message: text || response.statusText } as T
+  }
+
+  if (!response.ok) {
+    console.error('API Error:', {
+      status: response.status,
+      url,
+      data,
+    })
+    throw new Error(
+      (data as { errMsg?: string; message?: string })?.errMsg ||
+        (data as { message?: string })?.message ||
+        `Request failed with status ${response.status}`,
+    )
+  }
+
+  return data
+}
+
+// GET request
+export function get<T = unknown>(url: string, params?: Record<string, string | number | boolean>) {
+  const filteredParams = params
+    ? Object.fromEntries(
+        Object.entries(params).filter(([, v]) => v !== undefined && v !== null),
+      )
+    : undefined
+  const queryString =
+    filteredParams && Object.keys(filteredParams).length > 0
+      ? `?${new URLSearchParams(filteredParams as Record<string, string>).toString()}`
+      : ''
+  return request<T>(url + queryString, { method: 'GET' })
+}
+
+// POST request
+export function post<T = unknown>(url: string, data?: unknown) {
+  return request<T>(url, {
+    method: 'POST',
+    body: JSON.stringify(data),
+  })
+}