Use root relative link and directory-style URL for plain text nodes

- Use root relative link instead of directory-relative URL which caused tags to be appended to the on-page tags for plaintext nodes.
- Use directory-style URLs instead of appending .html to match the implementation for badges.

Author: AnneCYH

src/sphinx_tags/__init__.py

@@ -115,8 +115,8 @@ def _get_plaintext_node(
         self, tag: str, file_basename: str, relative_tag_dir: Path
     ) -> List[nodes.Node]:
         """Get a plaintext reference link for the given tag"""
-        link = relative_tag_dir / f"{file_basename}.html"
-        return nodes.reference(refuri=str(link), text=tag)
+        link = Path(self.env.app.config.tags_output_dir) / f"{file_basename}/"
+        return nodes.reference(refuri="/" + str(link), text=tag)
 
     def _get_badge_node(
         self, tag: str, file_basename: str, relative_tag_dir: Path