Fix proxy auth for persistent browser contexts

Chromium's --proxy-server CLI flag silently ignores inline credentials
(user:pass@server). For persistent contexts, crawl4ai was embedding
credentials in this flag via ManagedBrowser.build_browser_flags(),
causing proxy auth to fail and the browser to fall back to direct
connection.

Fix: Use Playwright's launch_persistent_context(proxy=...) API instead
of subprocess + CDP when use_persistent_context=True. This handles
proxy authentication properly via the HTTP CONNECT handshake. The
non-persistent and CDP paths remain unchanged.

Changes:
- Strip credentials from --proxy-server flag in build_browser_flags()
- Add launch_persistent_context() path in BrowserManager.start()
- Add cleanup path in BrowserManager.close()
- Guard create_browser_context() when self.browser is None
- Add regression tests covering all 4 proxy/persistence combinations

tests/proxy/test_persistent_proxy.py

@@ -0,0 +1,68 @@
+import asyncio
+import os
+import shutil
+import uuid
+from crawl4ai import AsyncWebCrawler, BrowserConfig, CrawlerRunConfig
+from crawl4ai.async_configs import ProxyConfig
+
+
+async def crawl_chanel(url: str):
+    profile_dir = os.path.expanduser(f"~/.crawl4ai/chanel_{uuid.uuid4().hex[:8]}")
+    os.makedirs(profile_dir, exist_ok=True)
+
+    browser_config = BrowserConfig(
+        headless=True,
+        enable_stealth=True,
+        use_persistent_context=True,
+        user_data_dir=profile_dir,
+        viewport_width=1920,
+        viewport_height=1080,
+        user_agent="Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/122.0.0.0 Safari/537.36",
+        headers={
+            "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8",
+            "Accept-Language": "en-US,en;q=0.9",
+            "Sec-Fetch-Dest": "document",
+            "Sec-Fetch-Mode": "navigate",
+            "Sec-Fetch-Site": "none",
+            "Sec-Fetch-User": "?1",
+        },
+        proxy_config=ProxyConfig(
+            server="https://network.joinmassive.com:65535",
+            username="mpuQHs4sWZ-country-US",
+            password="D0yWxVQo8wQ05RWqz1Bn",
+        ),
+    )
+
+    run_config = CrawlerRunConfig(
+        magic=True,
+        simulate_user=True,
+        override_navigator=True,
+        page_timeout=120000,
+        wait_until="load",
+        delay_before_return_html=10.0,
+    )
+
+    try:
+        async with AsyncWebCrawler(config=browser_config) as crawler:
+            result = await crawler.arun(url, config=run_config)
+            return result
+    finally:
+        shutil.rmtree(profile_dir, ignore_errors=True)
+
+
+async def main():
+    url = "https://www.chanel.com/us/fashion/handbags/c/1x1x1/"
+    result = await crawl_chanel(url)
+    print(f"Status: {result.status_code}")
+    print(f"Success: {result.success}")
+    print(f"HTML: {len(result.html):,} bytes")
+    if result.markdown:
+        md_len = len(result.markdown.raw_markdown)
+        print(f"Markdown: {md_len:,} chars")
+        if md_len > 500:
+            print(f"\nFirst 500 chars of markdown:\n{result.markdown.raw_markdown[:500]}")
+    if result.error_message:
+        print(f"Error: {result.error_message}")
+
+
+asyncio.run(main())