chore(angular-react): Migrate ItemsComponent to React

[devin-ai-integration]

chore(angular-react): Migrate ItemsComponent to React

Summary

Migrates the Angular ItemsComponent (container component for the shop items list) to React. This is a 1:1 migration following the Angular-to-React playbook.

The React component:

• Uses useState hooks for items list and selected item state
• Renders items using .map() (replacing Angular's *ngFor)
• Implements conditional rendering for item detail (replacing *ngIf)
• Includes placeholder divs with TODO comments for child components (ItemComponent, ItemDetailComponent, AddItemComponent) that need to be migrated separately
• Preserves the same hardcoded default items as the Angular version

Note: This PR adds React component files but does not add React dependencies to package.json. The project will need React, @testing-library/react, and Jest configured before these files can compile/run.

Review & Testing Checklist for Human

• Verify React setup is planned: These files won't compile until React is added to package.json and tsconfig.json is updated with JSX support
• Confirm placeholder approach is acceptable: Child components use placeholder divs with TODO comments - verify this matches the incremental migration strategy
• Review state management: Check that useState for items and selectedItem aligns with expected behavior
• Test file is aspirational: The test file documents expected behavior but cannot run without React/Jest setup

Notes

• The Angular ItemsComponent is preserved and not modified
• Uses key={index} for item mapping - consider using a unique item identifier if items will be dynamically added/removed
• handleAddItem currently just logs to console (matches Angular's saveItem() behavior)

Link to Devin run: https://app.devin.ai/sessions/3f110c7af12e4ba4a1314700f73da9cd
Requested by: @milind-cognition

[devin-ai-integration]

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