Complete SAND-WP-0001: bootstrap Python dev workflow

Scaffold sandboxer package (src layout, typer CLI stub, pytest, ruff),
Makefile targets, and document install/test/lint/build commands in
AGENTS.md and stack-and-commands.md. Mark bootstrap workplan finished.

Makefile

@@ -0,0 +1,26 @@
+.DEFAULT_GOAL := help
+
+.PHONY: help setup test lint format build check cli-version
+
+help: ## List available make targets
+	@awk 'BEGIN {FS = ":.*## "}; /^[a-zA-Z0-9_.-]+:.*## / {printf "  %-16s %s\n", $$1, $$2}' $(MAKEFILE_LIST)
+
+setup: ## Sync dependencies into .venv
+	uv sync --all-groups
+
+test: ## Run the test suite
+	uv run pytest
+
+lint: ## Run ruff lint checks
+	uv run ruff check .
+
+format: ## Auto-format with ruff
+	uv run ruff format .
+
+build: ## Build wheel and sdist
+	uv build
+
+check: lint test ## Run lint and tests (CI gate)
+
+cli-version: ## Print CLI version (smoke test for entry point)
+	uv run sandboxer version