fix: Part C OutputType - use STRING instead of TEXT

Fixed AttributeError: OutputType has no attribute TEXT.
Correct enum values are: NUMERIC, STRING, BOOLEAN, JSON, LIST, TEXT_SUMMARY.

Affected placeholders:
- energy_deficit_surplus: OutputType.STRING
- intake_volatility: OutputType.STRING

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

backend/placeholder_registrations/nutrition_part_c.py

@@ -202,7 +202,7 @@ energy_deficit_surplus_metadata = PlaceholderMetadata(
     business_meaning="Leicht interpretierbarer Energie-Statusindikator. Vereinfacht Energiebilanz zu verständlichen Kategorien.",
     unit="state (string)",
     time_window="7d",
-    output_type=OutputType.TEXT,
+    output_type=OutputType.STRING,
     placeholder_type=PlaceholderType.INTERPRETED,
     format_hint="Einer von drei Statuswerten: 'deficit', 'maintenance', 'surplus'",
     example_output="deficit",
@@ -281,7 +281,7 @@ intake_volatility_metadata = PlaceholderMetadata(
     business_meaning="Konsistenz- und Adhärenzindikator für Ernährungsumsetzung. Zeigt, wie gleichmäßig die Kalorienaufnahme über die Zeit ist.",
     unit="category (string)",
     time_window="28d",
-    output_type=OutputType.TEXT,
+    output_type=OutputType.STRING,
     placeholder_type=PlaceholderType.INTERPRETED,
     format_hint="Einer von drei Werten: 'stable', 'moderate', 'high'",
     example_output="moderate",