Add Shadow DOM flattening and reorder js_code execution pipeline

- Add `flatten_shadow_dom` option to CrawlerRunConfig that serializes
  shadow DOM content into the light DOM before HTML capture. Uses a
  recursive serializer that resolves <slot> projections and strips
  only shadow-scoped <style> tags. Also injects an init script to
  force-open closed shadow roots via attachShadow patching.

- Move `js_code` execution to after `wait_for` + `delay_before_return_html`
  so user scripts run on the fully-hydrated page. Add `js_code_before_wait`
  for the less common case of triggering loading before waiting.

- Add JS snippet (flatten_shadow_dom.js), integration test, example,
  and documentation across all relevant doc files.

tests/general/test_flatten_shadow_dom.py

@@ -0,0 +1,84 @@
+"""Test flatten_shadow_dom feature — full comparison."""
+import asyncio
+from crawl4ai import AsyncWebCrawler, BrowserConfig, CrawlerRunConfig
+
+URL = "https://store.boschrexroth.com/en/us/p/hydraulic-cylinder-r900999011"
+
+
+async def run_test(label, bc, rc):
+    print(f"\n{'='*70}")
+    print(f"TEST: {label}")
+    print(f"{'='*70}")
+    async with AsyncWebCrawler(config=bc) as crawler:
+        result = await crawler.arun(URL, config=rc)
+
+    html = result.html or ""
+    cleaned = result.cleaned_html or ""
+    md = ""
+    if result.markdown and hasattr(result.markdown, "raw_markdown"):
+        md = result.markdown.raw_markdown or ""
+
+    print(f"  Success:      {result.success}")
+    print(f"  Raw HTML:     {len(html):>8} chars")
+    print(f"  Cleaned HTML: {len(cleaned):>8} chars")
+    print(f"  Markdown:     {len(md):>8} chars")
+
+    checks = {
+        "Product title":               "HYDRAULIC CYLINDER" in md,
+        "Part number (R900999011)":    "R900999011" in md,
+        "Product description":         "mill type design" in md.lower(),
+        "Feature: 6 types of mounting":"6 types of mounting" in md,
+        "Feature: safety vent":        "safety vent" in md.lower(),
+        "Product Description heading": "Product Description" in md,
+        "Technical Specs heading":     "Technical Specs" in md,
+        "Downloads heading":           "Downloads" in md,
+        "Specs table: CDH1":           "CDH1" in md,
+        "Specs table: 250 bar":        "250" in md,
+    }
+    print(f"\n  Content checks:")
+    passes = sum(1 for v in checks.values() if v)
+    for k, v in checks.items():
+        print(f"    {'PASS' if v else 'FAIL'}  {k}")
+    print(f"\n  Result: {passes}/{len(checks)} checks passed")
+
+    # Show product content section
+    for term in ["Product Description"]:
+        idx = md.find(term)
+        if idx >= 0:
+            print(f"\n  --- Product content section ---")
+            print(md[idx:idx+1500])
+    return result
+
+
+async def main():
+    bc = BrowserConfig(headless=True)
+
+    r1 = await run_test(
+        "BASELINE (no shadow flattening)",
+        bc,
+        CrawlerRunConfig(wait_until="load", delay_before_return_html=3.0),
+    )
+
+    r2 = await run_test(
+        "WITH flatten_shadow_dom=True",
+        bc,
+        CrawlerRunConfig(
+            wait_until="load",
+            delay_before_return_html=3.0,
+            flatten_shadow_dom=True,
+        ),
+    )
+
+    # Summary
+    md1 = r1.markdown.raw_markdown if r1.markdown else ""
+    md2 = r2.markdown.raw_markdown if r2.markdown else ""
+    print(f"\n{'='*70}")
+    print(f"SUMMARY")
+    print(f"{'='*70}")
+    print(f"  Baseline markdown:  {len(md1):>6} chars")
+    print(f"  Flattened markdown: {len(md2):>6} chars")
+    print(f"  Improvement:        {len(md2)/max(len(md1),1):.1f}x more content")
+
+
+if __name__ == "__main__":
+    asyncio.run(main())