Integrate categorization & stock steps with Tour system

- Updated WizardContext with new state management:
  - Added categorizedProducts and productsWithStock state
  - Added categorizationCompleted and stockEntryCompleted flags
  - Implemented updateCategorizedProducts() and updateProductsWithStock() methods
  - Updated getVisibleSteps() to include new steps in AI-assisted path

- Integrated ProductCategorizationStep and InitialStockEntryStep into UnifiedOnboardingWizard:
  - Added conditional rendering based on AI analysis completion
  - Wired up state management for both steps
  - Added intermediate update handlers

- Integrated Tour system at app level:
  - Added TourProvider to App.tsx context hierarchy
  - Added Tour component for rendering active tours
  - Added TourButton to Sidebar navigation
  - Tour button visible when sidebar is expanded

This completes the Phase 6.5 integration and sets up the guided tour infrastructure.

frontend/src/components/layout/Sidebar/Sidebar.tsx

@@ -12,6 +12,7 @@ import { Button } from '../../ui';
 import { Badge } from '../../ui';
 import { Tooltip } from '../../ui';
 import { Avatar } from '../../ui';
+import { TourButton } from '../../ui/Tour/TourButton';
 import {
   LayoutDashboard,
   Package,
@@ -811,6 +812,13 @@ export const Sidebar = forwardRef<SidebarRef, SidebarProps>(({
           </div>
         )}
 
+        {/* Tour Button */}
+        {!isCollapsed && (
+          <div className="px-4 pb-2">
+            <TourButton variant="button" />
+          </div>
+        )}
+
         {/* Navigation */}
         <nav className={clsx('flex-1 overflow-y-auto overflow-x-hidden', isCollapsed ? 'px-1 py-4' : 'p-4')}>
           <ul className={clsx(isCollapsed ? 'space-y-1 flex flex-col items-center' : 'space-y-2')}>