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)

backend/app/services/website_client.py

@@ -6,24 +6,13 @@ from urllib.parse import quote
 
 import httpx
 
+from app.utils.number import decimal_string
+
 
 class WebsiteError(RuntimeError):
     pass
 
 
-def decimal_string(value: Any) -> str:
-    if value is None or value == "":
-        return ""
-    try:
-        d = Decimal(str(value))
-    except (InvalidOperation, ValueError):
-        return str(value)
-    n = d.normalize()
-    if n == n.to_integral():
-        return str(n.quantize(Decimal("1")))
-    return format(n, "f")
-
-
 def parse_positive_decimal(value: Any) -> Decimal | None:
     if value is None or value == "":
         return None
@@ -111,6 +100,10 @@ class Sub2ApiWebsiteClient:
         self.auth_type = auth_type
         self.auth_config = auth_config
         self.timeout = timeout
+        self._client = httpx.Client(timeout=timeout)
+
+    def close(self) -> None:
+        self._client.close()
 
     def _url(self, path: str) -> str:
         prefix = f"/{self.api_prefix}" if self.api_prefix else ""
@@ -130,8 +123,7 @@ class Sub2ApiWebsiteClient:
         return headers
 
     def _request(self, method: str, path: str, body: Any = None) -> Any:
-        with httpx.Client(timeout=self.timeout) as client:
-            resp = client.request(method, self._url(path), json=body, headers=self._headers())
+        resp = self._client.request(method, self._url(path), json=body, headers=self._headers())
         resp.raise_for_status()
         if not resp.content:
             return None