* chore: remove development setup files from repository
Removes VERTEX_ENV_SETUP.md and setup_vertex_env.sh from the
repository as they are not referenced in documentation or tests.
These files were added in PR #15824 alongside the VertexAI Search
feature. The setup information is already well-documented in the
official docs at:
docs/my-website/docs/pass_through/vertex_ai_search_datastores.md
* docs: add poetry run python usage to CLAUDE.md and AGENTS.md