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.

AGENTS.md

@@ -156,6 +156,25 @@ get wrong.
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+## Developer workflow
+
+**Layout:** `src/sandboxer/` (package `sandboxer`), subpackages `api/`, `profiles/`,
+`extensions/`, `lifecycle/`. Tests in `tests/`.
+
+**Prerequisites:** Python 3.11+, [uv](https://docs.astral.sh/uv/).
+
+```bash
+make setup          # install deps into .venv
+make check          # lint + test — run before committing
+make test           # pytest
+make lint           # ruff check
+make format         # ruff format
+make build          # uv build
+make cli-version    # smoke test: sandboxer version
+```
+
+Canonical detail: `.claude/rules/stack-and-commands.md`.
+
 ---
 
 ## Workplan Convention (ADR-001)