feat(crossword): add 2025‑12‑21 puzzles and update output generators

- Introduce three new puzzle files for the 2025‑12‑21 theme
- Update main generator to include new data set
- Regenerate pool, report, RSS and theme outputs
- Clean up legacy JSON format in main file
- Ensure consistency across generated assets

out/theme.txt

@@ -1,10 +1,36 @@
-HAAGS
-EXPLOSIE
-DREIGEND
+KANAAL
+STEKEN
+RECORD
+RUIM
+ZAKEN
+BOTEN
+ENGELAND
+FRANSE
 BRIEFJES
+EXPLOSIE
+HAAGS
+INGANG
+GLAZEN
+DEUR
+TIJD
 BETALEN
 KESTER
 MAARTEN
+OMROEP
+WEST
+RAADSEL
 DADER
 SPOREN
-ZWEEDS
+TEGEN
+POLITIE
+CAMIEL
+JANSEN
+MUZIKALE
+DIEPGANG
+MOTTO
+KLANK
+KLOOF
+PLATFORM
+WEG
+BUMA
+CULT