fix: Prevent undefined rendering in reasoning translations

Fixed React error #306 (text content mismatch) caused by undefined values
in reasoning translations.

Root cause: Translation functions could return undefined when:
- Translation key doesn't exist
- reasoning_data has unexpected structure
- parameters are missing

Changes:
- Added defaultValue to all translation calls
- Added || fallback operators to ensure strings are always returned
- Added proper null/undefined checks with empty string fallbacks
- Enhanced getInsightDescription with multiple fallback levels

This ensures all translation functions return valid strings, preventing
React hydration mismatches and rendering errors on the dashboard.

frontend/src/hooks/useReasoningTranslation.ts

@@ -34,7 +34,8 @@ export function useReasoningTranslation() {
       return t('purchaseOrder.low_stock_detection', {
         supplier_name: 'Unknown',
         product_names_joined: 'Items',
-        days_until_stockout: 7
+        days_until_stockout: 7,
+        defaultValue: 'Purchase order required for inventory replenishment'
       });
     }
 
@@ -45,10 +46,11 @@ export function useReasoningTranslation() {
       ...parameters,
       product_names_joined: Array.isArray(parameters.product_names)
         ? parameters.product_names.join(', ')
-        : parameters.product_names || 'Items'
+        : parameters.product_names || 'Items',
+      defaultValue: `Purchase order: ${type}`
     };
 
-    return t(`purchaseOrder.${type}`, params);
+    return t(`purchaseOrder.${type}`, params) || `Purchase order: ${type}`;
   };
 
   /**
@@ -60,12 +62,17 @@ export function useReasoningTranslation() {
         product_name: 'Product',
         predicted_demand: 0,
         current_stock: 0,
-        confidence_score: 85
+        confidence_score: 85,
+        defaultValue: 'Production batch scheduled based on demand forecast'
       });
     }
 
     const { type, parameters } = reasoningData;
-    return t(`productionBatch.${type}`, parameters);
+    const params = {
+      ...parameters,
+      defaultValue: `Production batch: ${type}`
+    };
+    return t(`productionBatch.${type}`, params) || `Production batch: ${type}`;
   };
 
   /**
@@ -80,10 +87,11 @@ export function useReasoningTranslation() {
       ...consequenceData,
       affected_products_joined: Array.isArray(consequenceData.affected_products)
         ? consequenceData.affected_products.join(', ')
-        : consequenceData.affected_products || 'products'
+        : consequenceData.affected_products || 'products',
+      defaultValue: `Impact: ${consequenceData.type}`
     };
 
-    return t(`consequence.${consequenceData.type}`, params);
+    return t(`consequence.${consequenceData.type}`, params) || '';
   };
 
   /**
@@ -91,7 +99,7 @@ export function useReasoningTranslation() {
    */
   const translateSeverity = (severity?: string): string => {
     if (!severity) return '';
-    return t(`severity.${severity}`);
+    return t(`severity.${severity}`, { defaultValue: severity }) || '';
   };
 
   /**
@@ -99,7 +107,7 @@ export function useReasoningTranslation() {
    */
   const translateTrigger = (trigger?: string): string => {
     if (!trigger) return '';
-    return t(`triggers.${trigger}`);
+    return t(`triggers.${trigger}`, { defaultValue: trigger }) || '';
   };
 
   /**

frontend/src/pages/app/analytics/ai-insights/AIInsightsPage.tsx

@@ -137,13 +137,18 @@ const AIInsightsPage: React.FC = () => {
       }
 
       try {
-        return t(`${category}.${insight.reasoning_data.type}`, insight.reasoning_data.parameters);
+        const params = {
+          ...insight.reasoning_data.parameters,
+          defaultValue: insight.description || `${category}: ${insight.reasoning_data.type}`
+        };
+        const translated = t(`${category}.${insight.reasoning_data.type}`, params);
+        return translated || insight.description || `AI Insight: ${insight.reasoning_data.type}`;
       } catch (e) {
         // Fall back to description if translation key not found
-        return insight.description;
+        return insight.description || 'AI Insight';
       }
     }
-    return insight.description;
+    return insight.description || 'AI Insight';
   };
 
   return (