Add comprehensive sample repository with examples demonstrating Midashi usage

[Copilot]

This PR adds a comprehensive sample repository to demonstrate various usage patterns of the Midashi library for automatic heading hierarchy management.

What's Added

Sample Directory (/sample/)

• SimpleExample.tsx - Basic usage showing automatic heading progression (h1→h2→h3→h4)
• WebsiteExample.tsx - Realistic website layout converted from the original issue code with proper Midashi components
• ComprehensiveExample.tsx - Advanced patterns showcasing custom components using useCurrentLevel() and useNextLevel() hooks
• OriginalBrokenExample.tsx - Educational comparison showing problems that Midashi solves
• README.md - Detailed documentation with usage patterns and integration examples
• index.ts - Convenient exports for all examples

Key Improvements from Original Issue Code

• Fixed all classname → className attribute issues
• Converted manual heading hierarchy to automatic Midashi management
• Proper semantic structure using all Midashi components (Header, Nav, Main, Section, Article, Aside, Footer)
• Added comprehensive test coverage (/test/sample.test.tsx)

Examples Demonstrate

1. Automatic Heading Hierarchy: How components automatically determine their heading level based on nesting
2. Semantic HTML Integration: Using Midashi wrappers for semantic elements
3. Custom Components: Building reusable components with Midashi hooks
4. Real-world Patterns: Typical website layouts with proper document structure

Example Usage

import { Main, Section, H } from 'midashi';

function App() {
  return (
    <>
      <H>Page Title</H>           {/* Renders as h1 */}
      <Main>
        <H>Main Content</H>       {/* Renders as h2 */}
        <Section>
          <H>First Section</H>    {/* Renders as h3 */}
        </Section>
      </Main>
    </>
  );
}

Testing

• All examples include comprehensive test coverage
• Tests verify proper HTML structure and heading hierarchy
• 40 total tests passing (33 existing + 7 new)

Documentation

• Updated main README.md to reference the sample directory
• Each example includes detailed comments explaining the features
• Sample README provides integration patterns for popular frameworks

Fixes #12.

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