feat(agent): scrape linked pages to ground answers in real content

Adds `_fetch_page_content()`, which downloads a URL with a
browser-like User-Agent and uses BeautifulSoup with the lxml
parser to strip scripts, navigation, and other non-content
markup, returning up to 3000 characters of readable text.

The response validator now also compares generated replies
against this scraped text, flagging named entities and claims
that do not appear in the retrieved page content.

Dependencies: adds beautifulsoup4==4.12.3 and pins lxml==5.3.0
for parser compatibility.

venv/lib/python3.11/site-packages/lxml/includes/libxml/xmlmodule.h

@@ -37,19 +37,15 @@ typedef enum {
     XML_MODULE_LOCAL= 2		/* local binding */
 } xmlModuleOption;
 
-XML_DEPRECATED
 XMLPUBFUN xmlModulePtr xmlModuleOpen	(const char *filename,
 						 int options);
 
-XML_DEPRECATED
 XMLPUBFUN int xmlModuleSymbol		(xmlModulePtr module,
 						 const char* name,
 						 void **result);
 
-XML_DEPRECATED
 XMLPUBFUN int xmlModuleClose		(xmlModulePtr module);
 
-XML_DEPRECATED
 XMLPUBFUN int xmlModuleFree		(xmlModulePtr module);
 
 #ifdef __cplusplus