refactor: Remove frontend auto-generation logic, delegate to backend

ARCHITECTURAL CHANGE: Migrated from frontend-based code generation to
backend-based generation following best practices discovered in the orders
service implementation.

RATIONALE:
After investigating the codebase, found that the orders service already
implements proper backend auto-generation for order numbers (ORD-YYYYMMDD-####).
This approach is superior to frontend generation for several reasons:

1. **Uniqueness Guarantee**: Database-enforced uniqueness, no race conditions
2. **Sequential Numbering**: True sequential IDs per tenant per day
3. **Consistent Format**: Server-controlled format ensures consistency
4. **Audit Trail**: Full server-side logging and tracking
5. **Simplicity**: No complex frontend state management
6. **Performance**: One less re-render trigger in wizards

CHANGES MADE:

**InventoryWizard.tsx:**
- ❌ Removed: useRef, useEffect auto-generation logic
- ❌ Removed: SKU generation (SKU-{name}-{timestamp})
- ✅ Changed: SKU field to optional with new placeholder
- ✅ Updated: Tooltip to indicate backend generation
- ✅ Simplified: Removed unnecessary imports (useEffect, useRef)

**QualityTemplateWizard.tsx:**
- ❌ Removed: useRef, useEffect auto-generation logic
- ❌ Removed: Template code generation (TPL-{name}-{timestamp})
- ✅ Changed: Template code field to optional
- ✅ Updated: Placeholder text for clarity
- ✅ Simplified: Removed unnecessary imports

**CustomerOrderWizard.tsx:**
- ❌ Removed: useRef, useEffect auto-generation logic
- ❌ Removed: Order number generation (ORD-{timestamp})
- ✅ Changed: Order number field to read-only/disabled
- ✅ Updated: Shows "Auto-generated on save" placeholder
- ✅ Added: Tooltip explaining backend format (ORD-YYYYMMDD-####)

NEXT STEPS (Backend Implementation Required):
1. Inventory Service: Add SKU generation method (similar to order_number)
2. Production Service: Add template code generation for quality templates
3. Format suggestions:
   - SKU: "SKU-{TENANT_PREFIX}-{SEQUENCE}" or similar
   - Template Code: "TPL-{TYPE_PREFIX}-{SEQUENCE}"

BENEFITS:
- ✅ Eliminates all focus loss issues from auto-generation
- ✅ Removes complex state management from frontend
- ✅ Ensures true uniqueness at database level
- ✅ Better user experience with clear messaging
- ✅ Follows established patterns from orders service
- ✅ Cleaner, more maintainable code

This change completes the frontend simplification. Backend services now
need to implement generation logic similar to orders service pattern.

frontend/src/components/domain/unified-wizard/wizards/InventoryWizard.tsx

@@ -1,4 +1,4 @@
-import React, { useState, useEffect, useRef } from 'react';
+import React, { useState } from 'react';
 import { WizardStep, WizardStepProps } from '../../../ui/WizardModal/WizardModal';
 import { AdvancedOptionsSection } from '../../../ui/AdvancedOptionsSection';
 import Tooltip from '../../../ui/Tooltip/Tooltip';
@@ -11,8 +11,6 @@ interface WizardDataProps extends WizardStepProps {
 
 // Single comprehensive step with all fields
 const InventoryDetailsStep: React.FC<WizardDataProps> = ({ data, onDataChange }) => {
-  const hasGeneratedSkuRef = useRef(false);
-
   const [inventoryData, setInventoryData] = useState({
     // Required fields
     name: data.name || '',
@@ -80,27 +78,6 @@ const InventoryDetailsStep: React.FC<WizardDataProps> = ({ data, onDataChange })
     customFields: data.customFields || '',
   });
 
-  // Auto-generate SKU from name if not provided
-  // Only watches SKU field to avoid interfering with typing in name field
-  useEffect(() => {
-    // Only auto-generate SKU if:
-    // 1. We haven't generated before
-    // 2. SKU is empty
-    // 3. Name has at least 3 characters (so we can take substring)
-    if (!hasGeneratedSkuRef.current && !inventoryData.sku && inventoryData.name && inventoryData.name.length >= 3) {
-      hasGeneratedSkuRef.current = true;
-      const sku = `SKU-${inventoryData.name.substring(0, 3).toUpperCase()}-${Date.now().toString().slice(-4)}`;
-      const newData = { ...inventoryData, sku };
-      setInventoryData(newData);
-      onDataChange({ ...data, ...newData });
-    }
-
-    // If user manually clears the SKU, allow regeneration
-    if (hasGeneratedSkuRef.current && !inventoryData.sku) {
-      hasGeneratedSkuRef.current = false;
-    }
-  }, [inventoryData.sku]); // Only watch SKU, not name - prevents interference with typing
-
   // Update parent whenever local state changes
   const handleDataChange = (newInventoryData: any) => {
     setInventoryData(newInventoryData);
@@ -177,8 +154,8 @@ const InventoryDetailsStep: React.FC<WizardDataProps> = ({ data, onDataChange })
         <div className="grid grid-cols-1 md:grid-cols-2 gap-4">
           <div>
             <label className="block text-sm font-medium text-[var(--text-secondary)] mb-2">
-              SKU
-              <Tooltip content="Auto-generated from name, or enter custom SKU">
+              SKU (Optional)
+              <Tooltip content="Leave empty to auto-generate from backend, or enter custom SKU">
                 <Info className="inline w-4 h-4 ml-1 text-[var(--text-tertiary)]" />
               </Tooltip>
             </label>
@@ -186,7 +163,7 @@ const InventoryDetailsStep: React.FC<WizardDataProps> = ({ data, onDataChange })
               type="text"
               value={inventoryData.sku}
               onChange={(e) => handleDataChange({ ...inventoryData, sku: e.target.value })}
-              placeholder="SKU-XXX-1234"
+              placeholder="Leave empty for auto-generation"
               className="w-full px-3 py-2 border border-[var(--border-secondary)] rounded-lg focus:outline-none focus:ring-2 focus:ring-[var(--color-primary)] bg-[var(--bg-primary)] text-[var(--text-primary)]"
             />
           </div>