feat: add non-streaming LLM API, tool registry, and web_search tool

Replace SSE streaming with non-streaming JSON for Anthropic API.
Add llm_chat_tools() returning structured llm_response_t with text
and tool_use blocks. Implement tool registry with dispatch-by-name
and web_search tool via Brave Search API (direct + proxy support).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

main/CMakeLists.txt

@@ -13,6 +13,8 @@ idf_component_register(
         "cli/serial_cli.c"
         "ota/ota_manager.c"
         "proxy/http_proxy.c"
+        "tools/tool_registry.c"
+        "tools/tool_web_search.c"
     INCLUDE_DIRS
         "."
     REQUIRES