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/tests/test_skills_router.py

@@ -58,3 +58,31 @@ unsupported: true
     assert valid is False
     assert "unsupported" in message
     assert skill_name is None
+
+
+def test_validate_skill_frontmatter_reads_utf8_on_windows_locale(tmp_path, monkeypatch) -> None:
+    skill_dir = tmp_path / "demo-skill"
+    _write_skill(
+        skill_dir,
+        """---
+name: demo-skill
+description: "Curly quotes: \u201cutf8\u201d"
+---
+
+# Demo Skill
+""",
+    )
+
+    original_read_text = Path.read_text
+
+    def read_text_with_gbk_default(self, *args, **kwargs):
+        kwargs.setdefault("encoding", "gbk")
+        return original_read_text(self, *args, **kwargs)
+
+    monkeypatch.setattr(Path, "read_text", read_text_with_gbk_default)
+
+    valid, message, skill_name = VALIDATE_SKILL_FRONTMATTER(skill_dir)
+
+    assert valid is True
+    assert message == "Skill is valid!"
+    assert skill_name == "demo-skill"