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/hash.h

@@ -109,10 +109,6 @@ XMLPUBFUN void
 /*
  * Add a new entry to the hash table.
  */
-XMLPUBFUN int
-		xmlHashAdd		(xmlHashTablePtr hash,
-		                         const xmlChar *name,
-		                         void *userdata);
 XMLPUBFUN int
 		xmlHashAddEntry		(xmlHashTablePtr hash,
 		                         const xmlChar *name,
@@ -122,11 +118,6 @@ XMLPUBFUN int
 		                         const xmlChar *name,
 		                         void *userdata,
 					 xmlHashDeallocator dealloc);
-XMLPUBFUN int
-		xmlHashAdd2		(xmlHashTablePtr hash,
-		                         const xmlChar *name,
-		                         const xmlChar *name2,
-		                         void *userdata);
 XMLPUBFUN int
 		xmlHashAddEntry2	(xmlHashTablePtr hash,
 		                         const xmlChar *name,
@@ -138,12 +129,6 @@ XMLPUBFUN int
 		                         const xmlChar *name2,
 		                         void *userdata,
 					 xmlHashDeallocator dealloc);
-XMLPUBFUN int
-		xmlHashAdd3		(xmlHashTablePtr hash,
-		                         const xmlChar *name,
-		                         const xmlChar *name2,
-		                         const xmlChar *name3,
-		                         void *userdata);
 XMLPUBFUN int
 		xmlHashAddEntry3	(xmlHashTablePtr hash,
 		                         const xmlChar *name,
@@ -214,10 +199,6 @@ XMLPUBFUN void *
 /*
  * Helpers.
  */
-XMLPUBFUN xmlHashTablePtr
-		xmlHashCopySafe		(xmlHashTablePtr hash,
-					 xmlHashCopier copy,
-					 xmlHashDeallocator dealloc);
 XMLPUBFUN xmlHashTablePtr
 		xmlHashCopy		(xmlHashTablePtr hash,
 					 xmlHashCopier copy);