Fix Windows C# JSON parsing errors by normalizing paths

Normalize all paths to use forward slashes instead of backslashes to prevent
JSON parsing errors when Windows paths contain unescaped backslashes.
This affects PathUtils.uri_to_path() and PathUtils.get_relative_path().

Fixes JSONDecodeError: Invalid \escape and Expecting value errors in C# tests on Windows.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/solidlsp/ls_utils.py

@@ -131,7 +131,13 @@ class PathUtils:
             from urlparse import urlparse
         parsed = urlparse(uri)
         host = f"{os.path.sep}{os.path.sep}{parsed.netloc}{os.path.sep}"
-        return os.path.normpath(os.path.join(host, url2pathname(unquote(parsed.path))))
+        path = os.path.normpath(os.path.join(host, url2pathname(unquote(parsed.path))))
+
+        # Normalize backslashes to forward slashes for JSON compatibility
+        # This prevents JSON parsing errors when paths contain unescaped backslashes
+        path = path.replace("\\", "/")
+
+        return path
 
     @staticmethod
     def path_to_uri(path: str) -> str:
@@ -152,7 +158,10 @@ class PathUtils:
         returns `None` otherwise.
         """
         if PurePath(path).drive == PurePath(base_path).drive:
-            return str(PurePath(os.path.relpath(path, base_path)))
+            rel_path = str(PurePath(os.path.relpath(path, base_path)))
+            # Normalize backslashes to forward slashes for JSON compatibility
+            rel_path = rel_path.replace("\\", "/")
+            return rel_path
         return None