Make MyPy happy

Fixes for various type errors throw by mypy.

portal/main.py

@@ -6,7 +6,7 @@ bp = Blueprint("main", __name__)
 
 @bp.get("/", defaults={"_": ""})
 @bp.get("/<path:_>")
-def index(_: object) -> str:
+def index(_: str) -> str:
     """
     Serve the index page at /*, i.e. at any path below / and at / itself.