Add programmatic configuration API

[nicknisi]

Problem

Currently, users must provide secrets and configuration values through environment variables (process.env). This has several limitations:

• Security concerns with secrets in environment variables
• Doesn't work well across different JavaScript runtimes (Deno, Cloudflare Workers, etc.)
• No convenient way to integrate with secret management systems

Solution

This PR adds a new configure() function that enables programmatic configuration with multiple flexible patterns:

// in entry.server.tsx

// Direct values approach
configure({
  clientId: 'client_...',
  apiKey: 'sk_test_...',
  redirectUri: 'http://localhost:3000/callback',
  cookiePassword: 'secure-password...',
});

// Function-based for different environments (may not yet be fully supported)
configure(key => Deno.env.get(key));

// Hybrid approach
configure({ redirectUri: 'https://example.com/callback' }, mySecretSource);

Implementation Details

• Added lazy initialization to prevent eager loading of credentials
• Environment variables still take precedence (maintains backward compatibility)
• Centralized default values for optional settings
• Added TypeScript overloads for improved developer experience
• Documentation in README updated to explain the new configuration options

Benefits

• Improved security - credentials don't need to be exposed in environment variables
• Cross-platform support - works in any JavaScript runtime
• Better developer experience - flexible API with strong typing
• Secret management integration - values can be loaded from vault services

Testing

• Added unit tests for all configuration patterns
• Verified backward compatibility with environment variables

Additional Changes

• Lazily instantiates workos instance (parity with authkit-nextjs)
• exposes getWorkOS() function to user to get access to WorkOS instance (parity with authkit-nextjs)

Breaking Changes

None. This is a non-breaking enhancement that maintains compatibility with existing code.

Fixes #38

[dandorman]

This seems good to me. (I had a few comments, but nothing that should block this, imo.)

I think it would be great if something like this existed in the Node WorkOS client itself, but ... the perfect is the enemy of the good, and this is an excellent starting place that will improve devex for our Remix users.