feat(export): add csv/json article export with date relevance scoring

backend/tests/test_relevance.py

@@ -0,0 +1,21 @@
+from datetime import datetime, timezone
+import unittest
+
+from backend.app.relevance import article_age_days, article_relevance
+
+
+class TestRelevance(unittest.TestCase):
+    def test_article_age_and_relevance(self) -> None:
+        now = datetime(2026, 2, 18, 12, 0, 0, tzinfo=timezone.utc)
+        self.assertEqual(article_age_days("2026-02-18T10:00:00Z", now=now), 0)
+        self.assertEqual(article_relevance("2026-02-18T10:00:00Z", now=now), "hoch")
+
+        self.assertEqual(article_age_days("2026-02-14T12:00:00Z", now=now), 4)
+        self.assertEqual(article_relevance("2026-02-14T12:00:00Z", now=now), "mittel")
+
+        self.assertEqual(article_relevance("2025-12-01T00:00:00Z", now=now), "alt")
+        self.assertEqual(article_relevance(None, now=now), "unbekannt")
+
+
+if __name__ == "__main__":
+    unittest.main()