Add prefetch mode for two-phase deep crawling

- Add `prefetch` parameter to CrawlerRunConfig
- Add `quick_extract_links()` function for fast link extraction
- Add short-circuit in aprocess_html() for prefetch mode
- Add 42 tests (unit, integration, regression)

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

crawl4ai/utils.py

@@ -2461,6 +2461,54 @@ def normalize_url_tmp(href, base_url):
     return href.strip()
 
 
+def quick_extract_links(html: str, base_url: str) -> Dict[str, List[Dict[str, str]]]:
+    """
+    Fast link extraction for prefetch mode.
+    Only extracts <a href> tags - no media, no cleaning, no heavy processing.
+
+    Args:
+        html: Raw HTML string
+        base_url: Base URL for resolving relative links
+
+    Returns:
+        {"internal": [{"href": "...", "text": "..."}], "external": [...]}
+    """
+    from lxml.html import document_fromstring
+
+    try:
+        doc = document_fromstring(html)
+    except Exception:
+        return {"internal": [], "external": []}
+
+    base_domain = get_base_domain(base_url)
+    internal: List[Dict[str, str]] = []
+    external: List[Dict[str, str]] = []
+    seen: Set[str] = set()
+
+    for a in doc.xpath("//a[@href]"):
+        href = a.get("href", "").strip()
+        if not href or href.startswith(("#", "javascript:", "mailto:", "tel:")):
+            continue
+
+        # Normalize URL
+        normalized = normalize_url_for_deep_crawl(href, base_url)
+        if not normalized or normalized in seen:
+            continue
+        seen.add(normalized)
+
+        # Extract text (truncated for memory efficiency)
+        text = (a.text_content() or "").strip()[:200]
+
+        link_data = {"href": normalized, "text": text}
+
+        if is_external_url(normalized, base_domain):
+            external.append(link_data)
+        else:
+            internal.append(link_data)
+
+    return {"internal": internal, "external": external}
+
+
 def get_base_domain(url: str) -> str:
     """
     Extract the base domain from a given URL, handling common edge cases.