Add regression tests for the popularity/EV score

Ports tests/test_popularity_score.py from the Lotto sibling project
(same purpose: pin down known overplayed combinations scoring lower
than spread ones), adapted for 5 main numbers and adds coverage for
the Euro-number determinism bug fixed in 0285a1c (tips #1-3 used to
always return the identical pair). Also documents beautifulsoup4 as
a required dependency in the README, which was missing despite
update_from_eurojackpot_zahlen_eu.py needing it.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

documentation/ARCHITECTURE.md

@@ -159,3 +159,10 @@ Navigierbare Graph-Ansicht unter `graphify-out/`:
 
 Bei strukturellen Änderungen: `/graphify --update` zum inkrementellen
 Neuaufbau.
+
+## 7. Tests
+
+`tests/test_popularity_score.py` (pytest) prüft den Popularity/EV-Score
+gegen bekannte Vielspieler-Kombinationen (portiert von Lotto) und deckt
+außerdem den Euro-Zahlen-Determinismus-Bug ab (Tipps #1-3 lieferten früher
+immer dasselbe Paar). Ausführen mit `pytest tests/`.