feat: async AI calls, 10-min timeout, and failure messaging

- Make all AI endpoints (health scores + investment recommendations)
  fire-and-forget: POST returns immediately, frontend polls for results
- Extend AI API timeout from 2-5 min to 10 min for both services
- Add "last analysis failed — showing cached data" message to the
  Investment Recommendations panel (matches health score widgets)
- Add status/error_message columns to ai_recommendations table
- Remove nginx AI timeout overrides (no longer needed)
- Users can now navigate away during AI processing without interruption

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

nginx/default.conf

@@ -23,21 +23,8 @@ server {
         proxy_cache_bypass $http_upgrade;
     }
 
-    # AI recommendation endpoint needs a longer timeout (up to 3 minutes)
-    location /api/investment-planning/recommendations {
-        proxy_pass http://backend;
-        proxy_http_version 1.1;
-        proxy_set_header Upgrade $http_upgrade;
-        proxy_set_header Connection 'upgrade';
-        proxy_set_header Host $host;
-        proxy_set_header X-Real-IP $remote_addr;
-        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-        proxy_set_header X-Forwarded-Proto $scheme;
-        proxy_cache_bypass $http_upgrade;
-        proxy_read_timeout 180s;
-        proxy_connect_timeout 10s;
-        proxy_send_timeout 30s;
-    }
+    # AI endpoints now return immediately (async processing in background)
+    # No special timeout needed — kept for documentation purposes
 
     # Everything else -> Vite dev server (frontend)
     location / {