fix: complete remaining 8 optimization items

- HTTP connection pooling: UpstreamClient & WebsiteClient reuse httpx.Client
- Deduplicate decimal_string into shared app/utils/number.py
- Split scheduler transaction: snapshot write → webhook/website sync in separate sessions
- Remove hardcoded 170.106.100.210 migration from database.py
- Reset consecutive_failures on upstream update
- Healthcheck: install curl, replace python -c with curl -f
- Add .dockerignore to reduce build context
- Frontend: add axios-retry with exponential backoff (5xx/network errors only)

docker-compose.yml

@@ -17,7 +17,7 @@ services:
       - TZ=${TZ:-Asia/Shanghai}
       - UNHEALTHY_THRESHOLD=${UNHEALTHY_THRESHOLD:-3}
     healthcheck:
-      test: ["CMD", "python", "-c", "import urllib.request; urllib.request.urlopen('http://localhost:8000/healthz', timeout=5).read()"]
+      test: ["CMD", "curl", "-f", "http://localhost:8000/healthz"]
       interval: 30s
       timeout: 10s
       retries: 3