统一描述，大写环境变量。

pdf2zh/converter.py

@@ -395,7 +395,7 @@ class TextConverter(PDFConverter[AnyIO]):
             self.translator: BaseTranslator = AzureTranslator(
                 service, lang_out, lang_in, None
             )
-        elif param[0] == "tmt":
+        elif param[0] == "tencent":
             self.translator: BaseTranslator = TencentTranslator(
                 service, lang_out, lang_in, None
             )

pdf2zh/translator.py

@@ -70,8 +70,8 @@ class TencentTranslator(BaseTranslator):
             server_url = (
                 "tmt.tencentcloudapi.com"
             )
-            self.secret_id = os.getenv("Tencent_SECRET_ID")
-            self.secret_key = os.getenv("Tencent_SECRET_KEY")
+            self.secret_id = os.getenv("TENCENT_SECRET_ID")
+            self.secret_key = os.getenv("TENCENT_SECRET_KEY")
             
         except KeyError as e:
             missing_var = e.args[0]