Add BNB Swap Protocol - Complete DEX Application Example

[aniketsahu115]

Description

This PR adds a comprehensive token swap application example for the BNB Chain Cookbook Challenge under the Swap Protocol category (#11). The example demonstrates building a complete decentralized exchange interface on BSC with PancakeSwap integration.

Summary of Changes

• Added complete swap protocol implementation with smart contracts and frontend
• Integrated PancakeSwap Router V2 for token swapping functionality
• Implemented custom fee mechanism with owner controls (0.25% configurable)
• Created React frontend with Web3 wallet integration and real-time price quotes
• Added comprehensive documentation and setup guides
• Included security best practices with OpenZeppelin libraries

Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How Has This Been Tested?

• Smart contracts compiled successfully with Hardhat
• Deployed and tested on BSC Testnet
• Frontend application tested with MetaMask wallet connection
• Token swap functionality verified end-to-end
• Gas optimization and security features validated
• All documentation verified for accuracy and completeness

Technical Implementation

• Smart Contracts: Solidity 0.8.19 with security patterns
• Frontend: React 18 + Vite + Tailwind CSS + ethers.js v6
• Integration: PancakeSwap Router for liquidity access
• Security: Reentrancy protection and access controls

Learning Value

This example teaches developers DeFi protocol integration, smart contract security implementation, Web3 frontend development, and professional DeFi application architecture.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes