fix: correct nullable resolved directory annotation (#3771)

Assisted-by: GitHub Copilot (model: GPT-5.6 Sol, autonomous)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/specify_cli/agents.py

@@ -599,7 +599,7 @@ class CommandRegistrar:
         source_dir: Path,
         project_root: Path,
         context_note: Optional[str] = None,
-        _resolved_dir: Path = None,
+        _resolved_dir: Optional[Path] = None,
         link_outputs: bool = False,
         extension_id: Optional[str] = None,
     ) -> List[str]: