Add comprehensive code examples for JavaScript concepts

[TheCyperpunk]

🎯 Description

This PR addresses Issue #618: Add Examples by adding comprehensive, runnable JavaScript code examples for the 33 JavaScript concepts.

✨ What's Included

Code Examples (13 files)

• ✅ 01-call-stack.js - Call stack mechanics and LIFO behavior
• ✅ 02-primitive-types.js - All 7 primitive types with examples
• ✅ 03-value-vs-reference.js - Value vs reference type behavior
• ✅ 04-type-coercion.js - Type coercion and duck typing patterns
• ✅ 05-equality-comparison.js - == vs === vs typeof operators
• ✅ 06-scope.js - Function, block, and lexical scope
• ✅ 07-expression-vs-statement.js - Expressions vs statements
• ✅ 08-iife-modules.js - IIFE and module patterns
• ✅ 09-event-loop.js - Event loop and message queue
• ✅ 10-timers.js - setTimeout, setInterval, debounce, throttle
• ✅ 21-closures.js - Closure patterns and private variables
• ✅ 25-promises.js - Promise patterns and chaining
• ✅ 26-async-await.js - Async/await patterns

Documentation (4 files)

• ✅ examples/README.md - Overview and usage instructions
• ✅ examples/CONTRIBUTING_EXAMPLES.md - Contribution guidelines
• ✅ examples/QUICK_START.md - Beginner's quick start guide
• ✅ HACKTOBERFEST_CONTRIBUTION.md - Contribution summary

📊 Statistics

• 130+ practical examples covering 13 JavaScript concepts
• 2,500+ lines of clean, executable code
• Zero dependencies - all examples run with Node.js
• Well-structured - progressive complexity from basic to advanced

🎓 Educational Value

These examples help developers:

• Learn by doing with practical, runnable code
• Understand concepts through progressive examples
• Master fundamentals with clear, concise demonstrations
• Build confidence with tested, working code

🧪 Testing

All examples have been tested with:

• ✅ Node.js v18+
• ✅ No syntax errors
• ✅ No runtime errors
• ✅ Clear, informative output

How to Test

# Test individual example
node examples/01-call-stack.js

# Test all examples
for file in examples/*.js; do node "$file"; done

[TheCyperpunk]

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💬 Optional Comment After PR Creation

Hi maintainers! 👋

I've added comprehensive code examples for 13 JavaScript concepts to help developers learn through practical, runnable code. Each example file contains multiple demonstrations progressing from basic to advanced usage.

All examples are:
- ✅ Tested and working
- ✅ Clean and readable (no comment clutter)
- ✅ Self-contained (no dependencies)
- ✅ Educational and practical

I'm happy to:
- Add more examples for the remaining 20 concepts
- Make any changes based on your feedback
- Add additional documentation if needed

Looking forward to your review! 🚀