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/tatlock_core/toolset.py

@@ -55,17 +55,8 @@ time_difference_tool = Tool(
     ),
 )
 
-web_search_tool = Tool(
-    function=tools.search_web,
-    name="search_web",
-    description=(
-        "Search the web using SearXNG for current information. "
-        "Use this to find recent events, current data, or verify facts. "
-        "Returns formatted results with titles, URLs, and snippets. "
-        "Useful for information that may have changed since training data."
-    ),
-    takes_ctx=False,
-)
+# NOTE: Web search has been moved to The Librarian agent.
+# Use delegate_to_librarian(task="search web for ...") for web search.
 
 
 # Combined toolset of all core tools
@@ -74,7 +65,6 @@ tatlock_core_tools = [
     current_datetime_tool,
     time_offset_tool,
     time_difference_tool,
-    web_search_tool,
 ]