feat: migrate web search from tatlock_core to Librarian

Move web search functionality to The Librarian agent, integrating with
the library-desk /rag/search endpoint for enhanced search capabilities.

Changes:
- Add search_web, read_url, read_urls_batch tools to Librarian
- Add WebSearchResult, ContentExtractionResult models to client
- Add search_web, extract_content, extract_content_batch client methods
- Update Librarian capability with web/url/internet domains
- Remove search_web from tatlock_core tools and toolset
- Update Tatlock system prompt to delegate web search to Librarian
- Add comprehensive unit tests for new Librarian tools
- Clean up legacy src/agents/tools.py

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

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

src/agents/librarian/capability.py

@@ -21,10 +21,11 @@ LIBRARIAN_CAPABILITY = HouseholdCapability(
     role="The Librarian",
     category="research",
     description=(
-        "Research and wiki management: can CREATE wiki pages about topics "
+        "Research, web search, and wiki management: can SEARCH the web for current "
+        "information, READ URLs/articles, CREATE wiki pages about topics "
         "(with automatic HybridRAG research), UPDATE existing pages, "
-        "SEARCH wiki/knowledge graph/web, and synthesize information. "
-        "Use for: 'create a page about X', 'update wiki', 'find info on X'"
+        "and synthesize information from multiple sources. "
+        "Use for: 'search for X', 'what is X', 'create a page about X', 'read this URL'"
     ),
     domains=[
         "research",
@@ -33,6 +34,9 @@ LIBRARIAN_CAPABILITY = HouseholdCapability(
         "wiki",
         "documents",
         "search",
+        "web",
+        "url",
+        "internet",
         "synthesis",
         "create",
         "write",