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.

pyproject.toml

@@ -0,0 +1,39 @@
+[build-system]
+requires = ["hatchling"]
+build-backend = "hatchling.build"
+
+[project]
+name = "sandboxer"
+version = "0.0.0"
+description = "Sandbox provisioning meta-framework for Custodian"
+readme = "README.md"
+requires-python = ">=3.11"
+license = "MIT-0"
+dependencies = [
+    "typer>=0.12",
+]
+
+[project.scripts]
+sandboxer = "sandboxer.cli:app"
+
+[tool.hatch.build.targets.wheel]
+packages = ["src/sandboxer"]
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]
+pythonpath = ["src"]
+addopts = "-ra --strict-markers --strict-config"
+
+[tool.ruff]
+src = ["src", "tests"]
+target-version = "py311"
+line-length = 100
+
+[tool.ruff.lint]
+select = ["E", "F", "I", "UP", "B", "SIM"]
+
+[dependency-groups]
+dev = [
+    "pytest>=8.0",
+    "ruff>=0.6",
+]