feat: 医生端Web后台 + SignalR实时问诊

- 新增 doctor_web/ React前端 (dashboard/患者/问诊/报告/随访)
- 后端新增 doctor_endpoints (14个医生API) + ConsultationHub (SignalR)
- Flutter端 SignalR 替换轮询实现实时聊天

doctor_web/src/services/api-client.ts

@@ -0,0 +1,29 @@
+const BASE_URL = 'http://localhost:5000';
+
+async function request<T>(method: string, path: string, body?: unknown): Promise<T> {
+  const headers: Record<string, string> = { 'Content-Type': 'application/json' };
+
+  const res = await fetch(`${BASE_URL}${path}`, {
+    method,
+    headers,
+    body: body ? JSON.stringify(body) : undefined,
+  });
+
+  if (!res.ok) {
+    const text = await res.text();
+    throw new Error(text || `HTTP ${res.status}`);
+  }
+
+  const json = await res.json();
+  if (json.code !== 0) {
+    throw new Error(json.message || `Error code ${json.code}`);
+  }
+  return json.data as T;
+}
+
+export const api = {
+  get: <T>(path: string) => request<T>('GET', path),
+  post: <T>(path: string, body?: unknown) => request<T>('POST', path, body),
+  put: <T>(path: string, body?: unknown) => request<T>('PUT', path, body),
+  del: <T>(path: string) => request<T>('DELETE', path),
+};