fix: Add comprehensive null guards to all dashboard components

This commit fixes React Error #306 (text content mismatch) by ensuring
no component ever tries to render undefined values as text content.

Changes made across all dashboard components:

1. **Component Entry Guards**:
   - Added early returns for null/undefined data
   - Changed `if (loading)` to `if (loading || !data)` pattern
   - Components now show loading skeleton when data is undefined

2. **Property Access Guards**:
   - Added `|| fallback` operators for all rendered text
   - Added optional chaining for nested property access
   - Added conditional rendering for optional/array fields

3. **Specific Component Fixes**:

   **HealthStatusCard.tsx**:
   - Added early return for !healthStatus
   - Added fallback for status: `healthStatus.status || 'green'`
   - Added conditional rendering for nextScheduledRun
   - Added conditional rendering for checklistItems array
   - Added text fallback: `item.text || ''`

   **InsightsGrid.tsx**:
   - Added null check: `if (!insights || !insights.savings || ...)`
   - Added fallbacks: `insights.savings?.label || 'Savings'`
   - Added fallbacks for all 4 insight cards

   **OrchestrationSummaryCard.tsx**:
   - Added early return for !summary
   - Added fallback: `summary.message || ''`
   - Added fallback: `summary.runNumber || 0`
   - Added array checks: `summary.purchaseOrdersSummary && ...`
   - Added fallbacks for PO items: `po.supplierName || 'Unknown Supplier'`
   - Added fallbacks for batch items: `batch.quantity || 0`
   - Added safe date parsing: `batch.readyByTime ? new Date(...) : 'TBD'`

   **ProductionTimelineCard.tsx**:
   - Added early return for !timeline
   - Added array check: `!timeline.timeline || timeline.timeline.length === 0`
   - Added fallbacks for all item properties:
     - `item.statusIcon || '🔵'`
     - `item.productName || 'Product'`
     - `item.quantity || 0`
     - `item.unit || 'units'`
     - `item.batchNumber || 'N/A'`
     - `item.priority || 'NORMAL'`
     - `item.statusText || 'Status'`
     - `item.progress || 0`

   **ActionQueueCard.tsx**:
   - Added early return for !actionQueue
   - Added safe config lookup with fallback to normal urgency
   - Added array check: `!actionQueue.actions || ...`
   - Added property fallbacks:
     - `action.title || 'Action Required'`
     - `action.urgency || 'normal'`
     - `action.subtitle || ''`
     - `action.estimatedTimeMinutes || 5`
   - Added array guard: `(action.actions || []).map(...)`
   - Added fallbacks for counts: `actionQueue.totalActions || 0`

   **useReasoningTranslation.ts**:
   - Enhanced formatPOAction with explicit fallbacks
   - Enhanced formatBatchAction with explicit fallbacks
   - All translation functions return strings with || operators

   **DashboardPage.tsx**:
   - Removed conditional rendering operators (&&)
   - Components now always render and handle their own null states
   - Pattern: `<Component data={data} loading={loading} />`

4. **Testing Strategy**:
   - All components gracefully handle undefined data
   - Loading states shown when data is undefined
   - No undefined values can be rendered as text content
   - Multiple fallback layers ensure strings are always returned

This comprehensive fix addresses the root cause of React Error #306
by making all components bulletproof against undefined values.

frontend/src/components/dashboard/InsightsGrid.tsx

@@ -81,31 +81,36 @@ export function InsightsGrid({ insights, loading }: InsightsGridProps) {
     );
   }
 
+  // Guard against undefined values
+  if (!insights || !insights.savings || !insights.inventory || !insights.waste || !insights.deliveries) {
+    return null;
+  }
+
   return (
     <div className="grid grid-cols-1 sm:grid-cols-2 gap-4">
       <InsightCard
-        label={insights.savings.label}
-        value={insights.savings.value}
-        detail={insights.savings.detail}
-        color={insights.savings.color}
+        label={insights.savings?.label || 'Savings'}
+        value={insights.savings?.value || '€0'}
+        detail={insights.savings?.detail || 'This week'}
+        color={insights.savings?.color || 'green'}
       />
       <InsightCard
-        label={insights.inventory.label}
-        value={insights.inventory.value}
-        detail={insights.inventory.detail}
-        color={insights.inventory.color}
+        label={insights.inventory?.label || 'Inventory'}
+        value={insights.inventory?.value || '0%'}
+        detail={insights.inventory?.detail || 'Status'}
+        color={insights.inventory?.color || 'green'}
       />
       <InsightCard
-        label={insights.waste.label}
-        value={insights.waste.value}
-        detail={insights.waste.detail}
-        color={insights.waste.color}
+        label={insights.waste?.label || 'Waste'}
+        value={insights.waste?.value || '0%'}
+        detail={insights.waste?.detail || 'Reduction'}
+        color={insights.waste?.color || 'green'}
       />
       <InsightCard
-        label={insights.deliveries.label}
-        value={insights.deliveries.value}
-        detail={insights.deliveries.detail}
-        color={insights.deliveries.color}
+        label={insights.deliveries?.label || 'Deliveries'}
+        value={insights.deliveries?.value || '0%'}
+        detail={insights.deliveries?.detail || 'On-time'}
+        color={insights.deliveries?.color || 'green'}
       />
     </div>
   );