feat: add stealth mode and enhance undetected browser support

- Add playwright-stealth integration with enable_stealth parameter in BrowserConfig
- Merge undetected browser strategy into main async_crawler_strategy.py using adapter pattern
- Add browser adapters (BrowserAdapter, PlaywrightAdapter, UndetectedAdapter) for flexible browser switching
- Update install.py to install both playwright and patchright browsers automatically
- Add comprehensive documentation for anti-bot features (stealth mode + undetected browser)
- Create examples demonstrating stealth mode usage and comparison tests
- Update pyproject.toml and requirements.txt with patchright>=1.49.0 and other dependencies
- Remove duplicate/unused dependencies (alphashape, cssselect, pyperclip, shapely, selenium)
- Add dependency checker tool in tests/check_dependencies.py

Breaking changes: None - all existing functionality preserved

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

docs/examples/undetected_simple_demo.py

@@ -0,0 +1,118 @@
+"""
+Simple Undetected Browser Demo
+Demonstrates the basic usage of undetected browser mode
+"""
+
+import asyncio
+from crawl4ai import (
+    AsyncWebCrawler, 
+    BrowserConfig, 
+    CrawlerRunConfig,
+    UndetectedAdapter
+)
+from crawl4ai.async_crawler_strategy import AsyncPlaywrightCrawlerStrategy
+
+async def crawl_with_regular_browser(url: str):
+    """Crawl with regular browser"""
+    print("\n[Regular Browser Mode]")
+    browser_config = BrowserConfig(
+        headless=False,
+        verbose=True,
+    )
+    
+    async with AsyncWebCrawler(config=browser_config) as crawler:
+        result = await crawler.arun(
+            url=url,
+            config=CrawlerRunConfig(
+                delay_before_return_html=2.0
+            )
+        )
+        
+        print(f"Success: {result.success}")
+        print(f"Status: {result.status_code}")
+        print(f"Content length: {len(result.markdown.raw_markdown)}")
+        
+        # Check for bot detection keywords
+        content = result.markdown.raw_markdown.lower()
+        if any(word in content for word in ["cloudflare", "checking your browser", "please wait"]):
+            print("⚠️  Bot detection triggered!")
+        else:
+            print("✅ Page loaded successfully")
+        
+        return result
+
+async def crawl_with_undetected_browser(url: str):
+    """Crawl with undetected browser"""
+    print("\n[Undetected Browser Mode]")
+    browser_config = BrowserConfig(
+        headless=False,
+        verbose=True,
+    )
+    
+    # Create undetected adapter and strategy
+    undetected_adapter = UndetectedAdapter()
+    crawler_strategy = AsyncPlaywrightCrawlerStrategy(
+        browser_config=browser_config,
+        browser_adapter=undetected_adapter
+    )
+    
+    async with AsyncWebCrawler(
+        crawler_strategy=crawler_strategy,
+        config=browser_config
+    ) as crawler:
+        result = await crawler.arun(
+            url=url,
+            config=CrawlerRunConfig(
+                delay_before_return_html=2.0
+            )
+        )
+        
+        print(f"Success: {result.success}")
+        print(f"Status: {result.status_code}")
+        print(f"Content length: {len(result.markdown.raw_markdown)}")
+        
+        # Check for bot detection keywords
+        content = result.markdown.raw_markdown.lower()
+        if any(word in content for word in ["cloudflare", "checking your browser", "please wait"]):
+            print("⚠️  Bot detection triggered!")
+        else:
+            print("✅ Page loaded successfully")
+        
+        return result
+
+async def main():
+    """Demo comparing regular vs undetected modes"""
+    print("🤖 Crawl4AI Undetected Browser Demo")
+    print("="*50)
+    
+    # Test URLs - you can change these
+    test_urls = [
+        "https://www.example.com",  # Simple site
+        "https://httpbin.org/headers",  # Shows request headers
+    ]
+    
+    for url in test_urls:
+        print(f"\n📍 Testing URL: {url}")
+        
+        # Test with regular browser
+        regular_result = await crawl_with_regular_browser(url)
+        
+        # Small delay
+        await asyncio.sleep(2)
+        
+        # Test with undetected browser
+        undetected_result = await crawl_with_undetected_browser(url)
+        
+        # Compare results
+        print(f"\n📊 Comparison for {url}:")
+        print(f"Regular browser content: {len(regular_result.markdown.raw_markdown)} chars")
+        print(f"Undetected browser content: {len(undetected_result.markdown.raw_markdown)} chars")
+        
+        if url == "https://httpbin.org/headers":
+            # Show headers for comparison
+            print("\nHeaders seen by server:")
+            print("Regular:", regular_result.markdown.raw_markdown[:500])
+            print("\nUndetected:", undetected_result.markdown.raw_markdown[:500])
+
+if __name__ == "__main__":
+    asyncio.run(main())