Separate MCP SDK exports into dedicated submodule

[koistya]

This PR reorganizes the package exports to make it clearer that browserAuth() and related functionality are specifically designed for Model Context Protocol (MCP) SDK integration.

Closes #16, Closes #20

What changed

New module structure

• Created src/mcp.ts as a dedicated entry point for MCP SDK-specific exports
• Added oauth-callback/mcp export path in package.json
• Moved MCP-specific exports (browserAuth) to the new module
• Added namespace export (mcp) to main module for backward compatibility

Exported types

The MCP module now exports all necessary types for advanced usage:

• BrowserAuthOptions - Configuration options for browser OAuth flows
• Tokens - OAuth token storage interface
• TokenStore - Minimal storage interface for OAuth tokens
• ClientInfo - Dynamic client registration data (RFC 7591)
• OAuthSession - Active OAuth flow state for crash recovery
• OAuthStore - Full OAuth state storage interface

Why this change

1. Clarity: Makes it explicit that browserAuth() is designed for MCP SDK integration, not general OAuth usage
2. Organization: Separates core OAuth functionality from MCP-specific features
3. Type exports: Addresses missing type exports needed for custom implementations (Export missing TypeScript types for better integration support #16)
4. Module boundaries: Better separation of concerns between core and MCP functionality (Rename browserAuth() to mcpAuth() to reflect MCP SDK specificity #20)

How to use

For MCP SDK users (recommended)

// Direct import - cleaner and more explicit
import { browserAuth, fileStore } from "oauth-callback/mcp";

const authProvider = browserAuth({
  store: fileStore(),
});

Alternative: Namespace import

// Via namespace - all MCP functionality grouped
import { mcp } from "oauth-callback";

const authProvider = mcp.browserAuth({
  store: mcp.fileStore(),
});

For core OAuth functionality

// Core OAuth remains in main export
import { getAuthCode, OAuthError } from "oauth-callback";

const result = await getAuthCode("https://example.com/oauth/authorize?...");

Migration guide

If you're currently importing browserAuth from the main export:

Before:

import { browserAuth, fileStore } from "oauth-callback";

After:

import { browserAuth, fileStore } from "oauth-callback/mcp";

Or use the namespace approach to maintain similar import structure:

import { mcp } from "oauth-callback";
const { browserAuth, fileStore } = mcp;

Build changes

• Updated build script to compile both index.ts and mcp.ts separately
• Fixed Bun bundler crash when building multiple entry points simultaneously
• Both modules are now properly bundled (~56KB each)

Testing

• ✅ All 22 existing tests pass
• ✅ Build process works correctly with both modules
• ✅ Package validation (publint) passes
• ✅ Example code updated and tested
• ✅ TypeScript declarations properly generated

Breaking changes

⚠️ Potentially breaking: If you import browserAuth directly from "oauth-callback", you'll need to update your imports to use "oauth-callback/mcp" or the namespace export.

This change makes the package more maintainable and clearer about the intended use of each export.