fix: ImportError - normalize_signal_value does not exist

Root Cause:
- Tried to import normalize_signal_value from normalization_engine
- Function does not exist (only normalize_decision_signal)
- Caused 500 Internal Server Error on workflow execution

Backend workflow_executor.py:
- Changed import: normalize_signal_value → normalize_decision_signal
- normalize_decision_signal returns NormalizedSignal (not dict)
- Use returned object directly (no .get() calls)
- Simplified logic

Fix:
```python
# BEFORE (broken):
normalized = normalize_signal_value(...)
normalized_signals.append(NormalizedSignal(..., normalized.get('status')))

# AFTER (working):
normalized_signal = normalize_decision_signal(...)
normalized_signals.append(normalized_signal)
```

Issue: 500 Internal Server Error on workflow execution
Version: 0.9p (workflow module)
Part 3: End Node Template Engine - Import Fix

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

backend/workflow_executor.py

@@ -28,7 +28,7 @@ from question_augmenter import (
     parse_question_augmentations_from_jsonb
 )
 from result_container_parser import parse_result_container
-from normalization_engine import normalize_all_signals, normalize_signal_value, load_question_catalog
+from normalization_engine import normalize_all_signals, normalize_decision_signal, load_question_catalog
 from logic_evaluator import evaluate_logic_expression, resolve_signal_reference
 from join_evaluator import evaluate_join_node as evaluate_join_node_core
 from db import get_db, get_cursor
@@ -334,21 +334,15 @@ async def execute_node(
                         type_catalog_entry = catalog.get(q_config['type'], {})
 
                         # Normalize with question-specific spectrum
-                        normalized = normalize_signal_value(
+                        normalized_signal = normalize_decision_signal(
+                            question_type=signal_id,  # Use ID as question_type
                             raw_value=signal_value,
                             answer_spectrum=q_config['answer_spectrum'],
                             normalization_rules=type_catalog_entry.get('normalization_rules')
                         )
 
-                        normalized_signals.append(NormalizedSignal(
-                            question_type=signal_id,  # Store ID as question_type (for template access)
-                            raw_value=signal_value,
-                            normalized_value=normalized.get('normalized_value'),
-                            status=normalized.get('status'),
-                            confidence=normalized.get('confidence'),
-                            metadata=normalized.get('metadata')
-                        ))
-                        logger.debug(f"Node {node.id}: Normalized signal '{signal_id}' = '{signal_value}' → '{normalized.get('normalized_value')}'")
+                        normalized_signals.append(normalized_signal)
+                        logger.debug(f"Node {node.id}: Normalized signal '{signal_id}' = '{signal_value}' → '{normalized_signal.normalized_value}' (status: {normalized_signal.status})")
 
                 logger.info(f"Node {node.id}: Normalized {len(normalized_signals)} signals")