feat: complete Task 2.2 - test refresh pipeline with Snowflake data

Tested full refresh pipeline end-to-end with real Snowflake data:
- Fixed trust filter to read Name column from defaultTrusts.csv
- Fixed Decimal type handling in calculate_cost_per_patient_per_annum
- Fixed array handling in convert_to_records for average_administered
- Added required reference CSV files to data/ directory
- Configured Snowflake connection (account, warehouse, user)

Results:
- Snowflake fetch: 656,695 records in ~7s
- Transformations: 519,848 records after UPID/drug/directory
- Pathway nodes: 293 for all_6mo (8 trusts, 14 directories)
- Total processing time: ~6.2 minutes

analysis/statistics.py

@@ -153,7 +153,7 @@ def calculate_cost_per_patient_per_annum(
     patients with different treatment durations.
 
     Args:
-        total_cost: Total cost for the patient
+        total_cost: Total cost for the patient (can be Decimal or float)
         days_treated: Treatment duration as timedelta
 
     Returns:
@@ -171,7 +171,8 @@ def calculate_cost_per_patient_per_annum(
     if days <= 0:
         return None
 
-    return total_cost / (days / 365)
+    # Convert total_cost to float to handle Decimal from Snowflake
+    return float(total_cost) / (days / 365)
 
 
 def calculate_treatment_duration(