feat(observability): add structured application logging

Emit correlated JSON logs from the API and FunASR services, propagate request IDs to the client, and configure bounded opt-in Docker logging.

Document the host-wide Grafana/Loki query workflow and keep observability deployment ownership outside the application repository.

pages/feedback/index.wxml

@@ -6,7 +6,13 @@
   <text class="page-subtitle">填写课堂表现并保存到教学反馈记录。</text>
 
   <view wx:if="{{errorMessage}}" class="status-banner">
-    <text>{{errorMessage}}</text>
+    <view class="status-copy">
+      <text>{{errorMessage}}</text>
+      <view wx:if="{{errorRequestId}}" class="status-request-id">
+        <text>请求编号：{{errorRequestId}}</text>
+        <text class="status-action" bindtap="copyRequestId">复制</text>
+      </view>
+    </view>
     <text class="status-action" bindtap="retryLoad">重试</text>
   </view>