docs: add Obscura as a CDP backend example

docs/examples/obscura_cdp_backend.py

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+"""
+Use Obscura as a CDP backend for Crawl4AI.
+
+Obscura (https://github.com/h4ckf0r0day/obscura) is an open-source headless
+browser engine written in Rust. It runs JavaScript via V8 and speaks the Chrome
+DevTools Protocol, so Crawl4AI can drive it through the standard `cdp_url` path.
+It has no layout or paint engine, so it suits HTML and Markdown extraction rather
+than screenshots or PDFs.
+
+Setup:
+  1. Build Obscura: `OPENSSL_NO_VENDOR=1 cargo build --release`
+  2. Start the CDP server: `obscura serve --port 9222`
+     (it also serves the /json/version endpoint Crawl4AI uses to find the ws URL)
+  3. Run this script.
+
+The second URL below (quotes.toscrape.com/js) builds its content client-side, so
+crawling it exercises Obscura's JavaScript engine rather than just static HTML.
+
+Obscura rejects screenshot and PDF capture (no paint engine). Use a full Chromium
+for the visual leg if you need pixels.
+"""
+
+import asyncio
+
+from crawl4ai import AsyncWebCrawler, BrowserConfig, CrawlerRunConfig, CacheMode
+
+OBSCURA_CDP_URL = "http://127.0.0.1:9222"
+
+
+async def main():
+    browser_config = BrowserConfig(browser_mode="cdp", cdp_url=OBSCURA_CDP_URL)
+    run_config = CrawlerRunConfig(cache_mode=CacheMode.BYPASS)
+
+    async with AsyncWebCrawler(config=browser_config) as crawler:
+        for url in ["https://example.com", "https://quotes.toscrape.com/js/"]:
+            result = await crawler.arun(url=url, config=run_config)
+            print("-" * 40)
+            if result.success:
+                markdown = result.markdown.raw_markdown
+                print(f"{url}  (status {result.status_code}, {len(markdown)} chars)")
+                print(markdown[:200])
+            else:
+                print(f"{url}  failed: {result.error_message}")
+        print("-" * 40)
+
+
+if __name__ == "__main__":
+    asyncio.run(main())