fix: SyntaxError in placeholder_resolver.py line 1037

- Fixed unterminated string literal in get_placeholder_catalog()
- Line 1037 had extra quote: ('quality_sessions_pct', 'Qualitätssessions (%)'),'
- Should be: ('quality_sessions_pct', 'Qualitätssessions (%)'),

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/placeholder_resolver.py

@@ -1034,7 +1034,7 @@ def get_placeholder_catalog(profile_id: str) -> Dict[str, List[Dict[str, str]]]:
             ('trainingstyp_verteilung', 'Verteilung nach Trainingstypen'),
             ('training_minutes_week', 'Trainingsminuten pro Woche'),
             ('training_frequency_7d', 'Trainingshäufigkeit 7d'),
-            ('quality_sessions_pct', 'Qualitätssessions (%)'),'
+            ('quality_sessions_pct', 'Qualitätssessions (%)'),
             ('ability_balance_strength', 'Ability Balance - Kraft (0-100)'),
             ('ability_balance_endurance', 'Ability Balance - Ausdauer (0-100)'),
             ('proxy_internal_load_7d', 'Proxy Load 7d'),