feat: add OcrSettings scope configuration

src/polygateway/config.py

@@ -407,3 +407,29 @@ class EmbeddingSettings:
             normalize=bool(_cast(norm[1], "bool", norm[0])) if norm else False,
             expected_dim=expected_dim,
         )
+
+
+@dataclass(frozen=True)
+class OcrSettings:
+    """OCR scope 装配配置(M3 设计 §3.4): 复用 GatewaySettings,无 OCR 专用键。
+
+    cache/structured/pricing 键对 OCR 无意义,装配时忽略;TPM 闸不启用
+    (tpm=0)、看门狗键不配(非流式)由源键缺省自然达成。api_key 惯例填
+    "none"(MonkeyOCR 无鉴权,SourceConfig 非空校验用占位)。
+    """
+
+    gateway: GatewaySettings
+
+    @classmethod
+    def from_env(
+        cls,
+        scope: str = "OCR",
+        env: Mapping[str, str] | None = None,
+        *,
+        env_file: str = ".env",
+    ) -> OcrSettings:
+        if env is None:
+            env = {
+                k: v for k, v in {**dotenv_values(env_file), **os.environ}.items() if v is not None
+            }
+        return cls(gateway=GatewaySettings.from_env(scope.upper(), env=env))