feat: Migrate Header, Footer, and CommentCounter components to React

[devin-ai-integration]

feat: Migrate Header, Footer, and CommentCounter components to React

Summary

Continues the Angular-to-React migration by extracting inline template elements into separate React components. This PR creates three new React components following the established bridge pattern:

• Header: Extracts the <h3>Hello World!</h3> into a reusable component with configurable title prop
• Footer: Adds a new footer component displaying migration example text
• CommentCounter: Creates a component that displays the total comment count with styled background

All components follow the existing pattern of presenter.js (React component) + index.js (Angular wrapper using reactToAngularComponent). The main template in app.module.js has been updated to use these new components instead of inline HTML.

Review & Testing Checklist for Human

• Verify app loads correctly - Navigate to http://localhost:3000 and confirm all three new components render properly
• Check for console errors - Look for any PropTypes warnings or bridge-related errors in browser console
• Test visual layout - Confirm header, comment counter (gray background), comment list, and footer all display as expected
• Verify comment counter accuracy - Ensure "Total Comments: 2" matches the actual number of comments displayed

Notes

• Uses deprecated React.PropTypes syntax (should be migrated to prop-types package in future)
• Template string binding for title uses nested quotes: title="'Hello World!'" - may want to verify this syntax
• Demonstrates the bridge pattern working with both prop-less (Footer) and prop-based (Header, CommentCounter) components

Link to Devin run: https://app.devin.ai/sessions/45679905b5c14b92b1ade78ae666069a
Requested by: @benc-a11y

[devin-ai-integration]

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