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

src/puzzle/Main.java

@@ -4,6 +4,7 @@ import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Paths;
 import java.time.LocalDate;
+import java.util.Date;
 
 public class Main {
    // ---------------- CLI ----------------
@@ -76,7 +77,7 @@ public class Main {
 
       // Export to JSON file
       var dateStr = LocalDate.now().toString();
-      var theme = "algemeen";
+      var theme = "algemeen-" + new Date().getTime();
       var filename = String.format("crossword_%s_%02d_%s.json", dateStr, 1, safeSlug(theme));
       var outDir = "data";
       var outputPath = Paths.get(outDir, filename);