Port Python agentic search to Go (nav service, harness, tools) (#17702)

Port Python rag/advanced_rag agentic search to Go: ES-backed dataset-nav
service, agentic-search harness, and agent tools.

Includes agentic-search port plan and self-review docs.

.gitignore

@@ -222,12 +222,15 @@ backup
 
 /target
 
-# Do not include in PR (local dev / build artifacts)
+# Do not include in PR (local dev / build artifacts / working notes)
 ragflow.egg-info/
 uv-aarch64*.tar.gz
 uv-aarch64-unknown-linux-gnu.tar.gz
 docker/launch_backend_service_windows.sh
 
+# Scratch/working notes (agent task planning & self-review docs; not PR material)
+tasks/*.md
+
 # C++ build directories
 internal/binding/cpp/build/
 internal/binding/cpp/cmake-build-release/
@@ -239,6 +242,7 @@ internal/binding/cpp/cmake-build-debug/
 # Go server build output
 bin/*
 !bin/.gitkeep
+/ragflow_server
 .claude/settings.local.json
 
 .run/