Add make install for global sandboxer CLI

Document uv tool install path and uv run fallback so sandboxer is
available outside the project venv after make install.

.claude/rules/stack-and-commands.md

@@ -13,6 +13,13 @@ Run from the repo root. First-time setup:
 
 ```bash
 make setup          # uv sync --all-groups → .venv
+make install        # sandboxer → ~/.local/bin (ensure ~/.local/bin is on PATH)
+```
+
+Without global install, prefix commands with `uv run` from the repo root:
+
+```bash
+uv run sandboxer create --profile profile.compose-e2e --input repo=/path/to/repo
 ```
 
 Day-to-day verification (run before committing):