Fix template variable interpolation by creating params copy

Root cause: params = reasoning_data.get('parameters', {}) created a reference
to the dictionary instead of a copy. When modifying params to add
product_names_joined, the change didn't persist because the database object
was immutable/read-only.

Changes:
- dashboard_service.py:408 - Create dict copy for PO params
- dashboard_service.py:632 - Create dict copy for batch params
- Added clean_old_dashboard_data.py utility script to remove old POs/batches
  with malformed reasoning_data

The fix ensures template variables like {{supplier_name}}, {{product_names_joined}},
{{days_until_stockout}}, etc. are properly interpolated in the dashboard.

services/orchestrator/app/services/dashboard_service.py

@@ -404,8 +404,8 @@ class DashboardService:
             reasoning_type = reasoning_data.get('type', 'inventory_replenishment')
             reasoning_type_i18n_key = self._get_reasoning_type_i18n_key(reasoning_type, context="purchaseOrder")
 
-            # Preprocess parameters for i18n
-            params = reasoning_data.get('parameters', {})
+            # Preprocess parameters for i18n - MUST create a copy to avoid modifying immutable database objects
+            params = dict(reasoning_data.get('parameters', {}))
             # Convert product_names array to product_names_joined string
             if 'product_names' in params and isinstance(params['product_names'], list):
                 params['product_names_joined'] = ', '.join(params['product_names'])
@@ -629,7 +629,7 @@ class DashboardService:
                 "reasoning_data": reasoning_data,  # Structured data for i18n
                 "reasoning_i18n": {
                     "key": reasoning_type_i18n_key,
-                    "params": reasoning_data.get('parameters', {})
+                    "params": dict(reasoning_data.get('parameters', {}))  # Create a copy to avoid immutable object issues
                 },
                 "status_i18n": status_i18n  # i18n for status text
             })