feat: create smart contract builder's guide

Creates a comprehensive guide for building smart contracts on the PHPCoin platform.

The guide covers:
- Structural rules
- State management
- Annotations
- Core transaction templates
- Built-in utilities
- ERC20 token templates
- Deployment
- Command-line tools
- A series of examples from "Hello, World!" to a "Wrapped PHPCoin" token.

Author: google-labs-jules[bot]