fix: issue 1138 windows encoding (#1139)

* fix(windows): use utf-8 for text file operations

* fix(windows): normalize sandbox path masking

* fix(windows): preserve utf-8 handling after backend split

skills/public/image-generation/scripts/generate.py

@@ -33,7 +33,7 @@ def generate_image(
     output_file: str,
     aspect_ratio: str = "16:9",
 ) -> str:
-    with open(prompt_file, "r") as f:
+    with open(prompt_file, "r", encoding="utf-8") as f:
         prompt = f.read()
     parts = []
     i = 0