test(impressum): GT-Fixtures + Fix 'Telefonnummer' Pattern

Ground-Truth-Fixtures fuer 5 echte Impressums (ETO, Safetykon, BMW,
Elli, Hectronic). Pro Impressum:
  - text (User-eingegeben)
  - expected_clean (Felder die da sind → keine Findings)
  - business_scope
  - placement_concerns (Texte die deplatziert sind — fuer kommenden
    Cross-Placement-Agent)

13 GT-Tests + 11 Specialist-Tests = 24/24 gruen.

Bug-Fix: Elli schreibt 'Telefonnummer:' (kein 'Telefon:'),
mein Pattern matched nur Tel/Telefon. Erweitert:
'Tel(?:efon(?:nummer)?)?|Phone|Fon'

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend-compliance/compliance/services/specialist_agents/impressum/mcs.py

@@ -66,7 +66,8 @@ MCS: tuple[MC, ...] = (
         norm="§ 5 Abs. 1 Nr. 2 TMG",
         severity_if_missing="MEDIUM",
         patterns=(re.compile(
-            r"(?:Tel(?:efon)?|Phone)\.?\s*[:.\s]\s*[\+\d][\d\s/\-()]{5,}",
+            r"(?:Tel(?:efon(?:nummer)?)?|Phone|Fon)\.?\s*[:.\s]\s*"
+            r"[\+\d][\d\s/\-()]{5,}",
             re.IGNORECASE,
         ),),
     ),