fix: PLZ regex matches lowercase text and D-78467 format

Patterns ran on text.lower() but searched [A-Z] — changed to [a-z].
Also accept D-12345 prefix (common German format).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend-compliance/compliance/services/doc_checks/widerruf_checks.py

@@ -137,8 +137,8 @@ WIDERRUF_CHECKLIST = [
         "label": "Vollstaendige Adresse des Empfaengers",
         "level": 2, "parent": "recipient",
         "patterns": [
-            r"widerruf.*\d{5}\s+[A-Z\u00c0-\u017e]",
-            r"\d{5}\s+[A-Z\u00c0-\u017e]\w+.*widerruf",
+            r"widerruf.*(?:d[\-\s]?)?\d{5}\s+[a-z\u00c0-\u017e]",
+            r"(?:d[\-\s]?)?\d{5}\s+[a-z\u00c0-\u017e]\w+.*widerruf",
         ],
         "severity": "LOW",
     },