MCP Echo Env

# Project TODOs - [x] Add automated smoke test (see `tests/smoke.test.mjs`) to call `env_echo` with the SDK client and assert the returned payload contains `tool` and `variables` keys. - [x] Wire up a GitHub Actions workflow for lint, markdownlint, and the smoke test so publishing stays reliable. - [x] Document usage with additional MCP clients (Playwright MCP and Jina) to broaden coverage beyond Codex CLI. - [x] Revisit optional structured output schema so clients can rely on typed `variables` data. - [x] Explore lightweight logging controls or verbosity flags for noisy environments (`MCP_ECHO_ENV_LOG_LEVEL`). - [x] Add guidance for testing custom environment variables via `.env` files in multi-workspace setups.