This commit resolves the authentication issue where Auth::user() returns null
in MCP tool handlers when using the Dedicated HTTP transport mode.

## Problem Solved
- HTTP Integrated mode worked fine (uses Laravel's routing + middleware)
- HTTP Dedicated mode failed authentication (bypassed middleware stack)
- Tools couldn't access authenticated user context

## Solution Implemented
- McpAuthenticationMiddleware: Captures auth context from HTTP requests
- McpContext: Thread-safe storage for authentication data
- McpAuth facade: Laravel-style access to auth context in tools
- Enhanced transport controllers with automatic auth middleware
- Updated service provider with proper dependency registration

## Key Features
✅ Works with both HTTP transport modes (Integrated & Dedicated)
✅ Supports all authentication guards (Sanctum, API, Web)
✅ Automatic Bearer token authentication
✅ Zero breaking changes to existing code
✅ Comprehensive test coverage
✅ Proper security with context isolation

## Usage
```php
use PhpMcp\Laravel\Facades\McpAuth;

Mcp::tool('get_me', function () {
    // Works in both transport modes
    return McpAuth::user() ?? Auth::user();
});
```

## Files Added
- src/Http/Middleware/McpAuthenticationMiddleware.php
- src/Support/McpContext.php
- src/Facades/McpAuth.php
- tests/Feature/AuthenticationTest.php
- examples/AuthenticatedTools.php

## Files Modified
- src/Http/Controllers/*TransportController.php (auth integration)
- src/McpServiceProvider.php (service registration)
- config/mcp.php (default auth middleware)
- samples/basic/routes/mcp.php (usage example)

Fixes authentication issues in Dedicated HTTP configuration while maintaining
full backward compatibility and following Laravel coding standards.