feat: implement SDK class with capability composition

[prosdev]

Implements #6 - Task #6: SDK Class

Summary

The main SDK class that brings everything together! This is the integration piece that composes all capabilities into a functional plugin system.

Core SDK Features

• ✅ Plugin registration via use() with capability injection
• ✅ Event-based lifecycle (sdk:init, sdk:ready, sdk:destroy)
• ✅ Method chaining support (sdk.use().use().init())
• ✅ Delegates to capabilities (Config, Emitter)
• ✅ Proper initialization checks and cleanup

Capability Composition in use()

The magic happens in the use() method:

use(pluginFn: PluginFunction): this {
  // Create instances for this plugin
  const namespace = new Namespace();
  const expose = new Expose(this);
  
  // Compose Plugin object with all capabilities
  const plugin: Plugin = {
    ns: namespace.ns.bind(namespace),
    defaults: this.configInstance.defaults.bind(this.configInstance),
    on: this.emitter.on.bind(this.emitter),
    off: this.emitter.off.bind(this.emitter),
    emit: this.emitter.emit.bind(this.emitter),
    expose: expose.expose.bind(expose),
    mustEnable: () => this.configInstance.markRequired(namespace.name)
  };
  
  // Execute plugin with injected capabilities
  pluginFn(plugin, this, this.configInstance);
  
  return this;
}

Public API

Method	Description
use(pluginFn)	Register plugins
init()	Initialize SDK (idempotent)
destroy()	Clean up SDK
get/set()	Config access
on/off/emit()	Event handling
getAll()	Get all config
isReady()	Check initialization state

Usage Example

const sdk = new SDK({ name: 'my-sdk' });

sdk.use((plugin, instance, config) => {
  plugin.ns('analytics');
  plugin.defaults({ analytics: { endpoint: 'https://api.example.com' } });
  
  plugin.expose({
    track(event: string) {
      console.log('Tracking:', event);
    }
  });
  
  instance.on('sdk:ready', () => {
    console.log('Plugin ready!');
  });
});

await sdk.init();
sdk.track('page_view');

Testing

• 52 comprehensive tests
• 97.14% coverage on sdk.ts
• Integration scenarios:
  • Plugin communication via events
  • Config sharing between plugins
  • Lifecycle event handling
  • Multiple plugins working together

Additional Changes

• ✅ Added test:coverage script to package.json
• ✅ Excluded barrel files (index.ts, use.ts) from coverage
• ✅ Overall: 98.97% coverage, 192 tests passing
• ✅ Comprehensive README for core package

Documentation

Added complete README with:

• Quick start guide
• Plugin creation tutorial
• Core concepts and API reference
• Advanced patterns
• TypeScript support guide

Closes #6