UI improvements + add axis orientation test

- Rename app to 'Motief: de stematlas' in Home.py
- Remove PCA variance caption from compass tab
- Hardcode db_path and window_size; remove sidebar inputs
- Change trajectories default to [CDA, D66, VVD]
- Move quiz to pages/1_Stemwijzer.py; wrap in st.form
- Remove quiz tab from main explorer
- Add pytest dev dep + fix test fixtures (_load_mp_vectors_for_window)
- Add test_pca_axis_orientation with proper PCA variance dominance

pages/1_Stemwijzer.py

@@ -1,5 +1,13 @@
-"""Stemwijzer page — thin wrapper around the existing app module."""
+"""Stemwijzer page — quiz to find your matching MP."""
 
-from app import main  # noqa: F401  (module-level set_page_config runs on import)
+import streamlit as st
 
-main()
+st.set_page_config(
+    page_title="Stemwijzer",
+    page_icon="🗳️",
+    layout="centered",
+)
+
+from explorer import build_mp_quiz_tab
+
+build_mp_quiz_tab("data/motions.db")