feat: add axis classifier with party ideology reference data

classify_axes() correlates per-party PCA positions against party_ideologies.csv
to assign honest dynamic labels (Links-Rechts, Coalitie-Oppositie, etc.)
instead of always assuming the first PCA axis is left-right.

data/coalition_membership.csv

@@ -0,0 +1,51 @@
+window_id,party
+2012,VVD
+2012,PvdA
+2013,VVD
+2013,PvdA
+2014,VVD
+2014,PvdA
+2015,VVD
+2015,PvdA
+2016,VVD
+2016,PvdA
+2017,VVD
+2017,CDA
+2017,D66
+2017,ChristenUnie
+2018,VVD
+2018,CDA
+2018,D66
+2018,ChristenUnie
+2019,VVD
+2019,CDA
+2019,D66
+2019,ChristenUnie
+2020,VVD
+2020,CDA
+2020,D66
+2020,ChristenUnie
+2021,VVD
+2021,CDA
+2021,D66
+2021,ChristenUnie
+2022,VVD
+2022,D66
+2022,CDA
+2022,ChristenUnie
+2023,VVD
+2023,D66
+2023,CDA
+2023,ChristenUnie
+2024,PVV
+2024,VVD
+2024,NSC
+2024,BBB
+2025,PVV
+2025,VVD
+2025,NSC
+2025,BBB
+2026,PVV
+2026,VVD
+2026,NSC
+2026,BBB

data/party_ideologies.csv

@@ -0,0 +1,23 @@
+party,left_right,progressive
+VVD,0.65,0.10
+PvdA,-0.70,0.75
+SP,-0.90,0.50
+CDA,0.25,-0.45
+D66,-0.10,0.85
+GroenLinks,-0.70,0.90
+GL,-0.70,0.90
+GroenLinks-PvdA,-0.70,0.82
+ChristenUnie,0.10,-0.55
+SGP,0.35,-0.95
+PVV,0.90,-0.50
+DENK,-0.40,0.55
+50Plus,-0.05,-0.10
+FVD,0.90,-0.75
+PvdD,-0.60,0.85
+Volt,-0.20,0.80
+JA21,0.70,-0.30
+BBB,0.50,-0.35
+NSC,0.20,-0.20
+Nieuw Sociaal Contract,0.20,-0.20
+BVNL,0.85,-0.55
+Bij1,-0.90,0.90