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

backend/packages/harness/deerflow/skills/validation.py

@@ -25,7 +25,7 @@ def _validate_skill_frontmatter(skill_dir: Path) -> tuple[bool, str, str | None]
     if not skill_md.exists():
         return False, "SKILL.md not found", None
 
-    content = skill_md.read_text()
+    content = skill_md.read_text(encoding="utf-8")
     if not content.startswith("---"):
         return False, "No YAML frontmatter found", None