feat: enrich insights cards, add AI chatbot

Add 3 new data-driven insight cards (daily cases, district risk
comparison, weather impact) with real parquet data. Fix season
card to use current date instead of data date. Expand to 11 cards.

Add POST /api/chat endpoint proxying to ai.2890.ltd with JWT auth.
Create ChatBot frontend component with collapsible chat panel,
message bubbles, and auto-scroll. Chat API key stored in .env only.

Clean up duplicate typing imports in insights.py, export cachedPost.

frontend/src/pages/Insights.tsx

@@ -1,6 +1,7 @@
 import { useEffect } from 'react';
 import { useAnalysisStore } from '@/stores/analysisStore';
 import { ErrorBanner } from '@/components/ErrorBanner';
+import { ChatBot } from '@/components/ChatBot';
 import {
   Lightbulb,
   AlertTriangle,
@@ -193,6 +194,8 @@ export function Insights() {
           <p className="text-text-secondary">暂无洞察数据</p>
         </div>
       )}
+
+      <ChatBot />
     </div>
   );
 }