[Docs] Documentation Expansion for php-wasm/node (#2780)

## Summary

Transforms the minimal `php-wasm/node` documentation into a
comprehensive developer guide with practical examples, integration
patterns, and real-world use cases.

## Motivation

The existing documentation provided only a basic usage example and API
reference link, leaving developers without:
- Clear understanding of when and why to use `@php-wasm/node`
- Practical, copy-paste ready code examples
- Guidance on integrating with existing Node.js tooling
- Best practices for performance and error handling

This created friction for developers trying to adopt WordPress
Playground in Node.js environments.

## Changes

### 📚 Documentation Structure
- Added front matter (title, slug) for documentation site integration
- Organized content into logical sections with clear hierarchy
- Included 15+ working code examples across multiple scenarios

### 🎯 New Sections

#### Use Cases (8 categories)
Defines clear scenarios where `@php-wasm/node` provides value:
- Server-Side PHP Execution (CI/CD, testing, microservices)
- Data Processing & Transformation (CSV, JSON, SQLite, ZIP)
- Template Rendering & Content Generation
- API Development & Testing
- PHP Code Analysis & Testing
- Legacy Code Integration
- Educational Platforms
- WordPress Development Tools

#### Practical Demos (6 complete examples)
Working code demonstrations of common patterns:
1. **File System Operations** - Directory creation, file I/O, JSON
handling
2. **SQLite Database Operations** - Schema creation, CRUD operations,
queries
3. **Processing ZIP Archives** - Archive creation, inspection,
extraction
4. **HTTP Request/Response Pattern** - Simulating web server behavior
5. **Template Rendering Engine** - Dynamic HTML generation from
templates
6. **Real-time Code Execution & Streaming** - Streaming output handling


### 🔧 Technical Details
- All examples use ES modules syntax
- TypeScript examples included for type-safe implementations
- Code follows consistent formatting and style
- Examples are self-contained and immediately runnable

## Impact

**For Developers:**
- Provides ready-to-use patterns for common scenarios
- Demonstrates integration with popular Node.js tools

Author: fellyph