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

backend/app/relevance.py

@@ -0,0 +1,44 @@
+from __future__ import annotations
+
+from datetime import datetime, timezone
+
+
+def _parse_iso_datetime(value: str | None) -> datetime | None:
+    if not value:
+        return None
+    raw = value.strip()
+    if not raw:
+        return None
+    if raw.endswith("Z"):
+        raw = raw[:-1] + "+00:00"
+    try:
+        parsed = datetime.fromisoformat(raw)
+    except ValueError:
+        return None
+    if parsed.tzinfo is None:
+        parsed = parsed.replace(tzinfo=timezone.utc)
+    return parsed
+
+
+def article_age_days(published_at: str | None, now: datetime | None = None) -> int | None:
+    published = _parse_iso_datetime(published_at)
+    if not published:
+        return None
+    ref = now or datetime.now(timezone.utc)
+    delta = ref - published
+    if delta.total_seconds() < 0:
+        return 0
+    return delta.days
+
+
+def article_relevance(published_at: str | None, now: datetime | None = None) -> str:
+    days = article_age_days(published_at, now=now)
+    if days is None:
+        return "unbekannt"
+    if days <= 2:
+        return "hoch"
+    if days <= 7:
+        return "mittel"
+    if days <= 30:
+        return "niedrig"
+    return "alt"