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/stealth_test_simple.py

@@ -0,0 +1,62 @@
+"""
+Simple test to verify stealth mode is working
+"""
+
+import asyncio
+from crawl4ai import AsyncWebCrawler, BrowserConfig, CrawlerRunConfig
+
+
+async def test_stealth():
+    """Test stealth mode effectiveness"""
+    
+    # Test WITHOUT stealth
+    print("=== WITHOUT Stealth ===")
+    config1 = BrowserConfig(
+        headless=False,
+        enable_stealth=False
+    )
+    
+    async with AsyncWebCrawler(config=config1) as crawler:
+        result = await crawler.arun(
+            url="https://bot.sannysoft.com",
+            config=CrawlerRunConfig(
+                wait_until="networkidle",
+                screenshot=True
+            )
+        )
+        print(f"Success: {result.success}")
+        # Take screenshot
+        if result.screenshot:
+            with open("without_stealth.png", "wb") as f:
+                import base64
+                f.write(base64.b64decode(result.screenshot))
+            print("Screenshot saved: without_stealth.png")
+    
+    # Test WITH stealth
+    print("\n=== WITH Stealth ===")
+    config2 = BrowserConfig(
+        headless=False,
+        enable_stealth=True
+    )
+    
+    async with AsyncWebCrawler(config=config2) as crawler:
+        result = await crawler.arun(
+            url="https://bot.sannysoft.com",
+            config=CrawlerRunConfig(
+                wait_until="networkidle",
+                screenshot=True
+            )
+        )
+        print(f"Success: {result.success}")
+        # Take screenshot
+        if result.screenshot:
+            with open("with_stealth.png", "wb") as f:
+                import base64
+                f.write(base64.b64decode(result.screenshot))
+            print("Screenshot saved: with_stealth.png")
+    
+    print("\nCheck the screenshots to see the difference in bot detection results!")
+
+
+if __name__ == "__main__":
+    asyncio.run(test_stealth())