feat: add gateway client with env-driven assembly

Includes config aggregation for multi-source env keys, from_env and
from_settings factories with explicit shared-backend injection,
gather_bounded, top-level exports, tightened import-linter layers with
the gate removed from the Makefile, and the finalized .env.example.

src/polygateway/structured/json_repair.py

@@ -49,9 +49,7 @@ class JsonRepairStrategy:
         try:
             data = json.loads(repair_json(stripped))
         except (json.JSONDecodeError, ValueError) as exc:
-            raise ResultInvalidError(
-                "JSON 修复失败", raw_text=text, repair_error=str(exc)
-            ) from exc
+            raise ResultInvalidError("JSON 修复失败", raw_text=text, repair_error=str(exc)) from exc
         if self._normalize is not None:
             data = self._normalize(data)
         return data