032: fix missing awaits in translate datasource endpoints (#5,6,7)

Three sync functions called async SupersetClient methods without await:
  - get_datasource_columns(): get_dataset_detail + get_database (async)
  - fetch_available_datasources(): get_datasets (async)
  - Route handlers: both calls missing await

Converted to async functions + added awaits. Both endpoints now return
proper data instead of coroutine errors.

backend/src/plugins/translate/service_datasource.py

@@ -114,7 +114,7 @@ def detect_virtual_columns(columns: list[dict[str, Any]]) -> list[str]:
 
 # #region get_datasource_columns [C:3] [TYPE Function]
 # @BRIEF Fetch datasource column metadata from Superset and return structured response.
-def get_datasource_columns(
+async def get_datasource_columns(
     datasource_id: int,
     env_id: str,
     config_manager: ConfigManager,
@@ -128,7 +128,7 @@ def get_datasource_columns(
         raise ValueError(f"Superset environment '{env_id}' not found")
 
     client = SupersetClient(env_config)
-    dataset_detail = client.get_dataset_detail(datasource_id)
+    dataset_detail = await client.get_dataset_detail(datasource_id)
 
     database_info = dataset_detail.get("database", {})
     dialect = None
@@ -140,7 +140,7 @@ def get_datasource_columns(
     if dialect is None:
         database_id = dataset_detail.get("database_id")
         if database_id:
-            db_record = client.get_database(int(database_id))
+            db_record = await client.get_database(int(database_id))
             db_result = db_record.get("result", db_record) if isinstance(db_record, dict) else db_record
             dialect = get_dialect_from_database(db_result)
         else: