Ship installed no-key math demo and verify it from the wheel

[bordeauxred]

Why

The current no-key demo works from a repo clone, but the demo entry point is not available after a wheel install. First-time users should be able to run a useful demo immediately after pip install clawloop.

What

• Add package-resident demo module, e.g. clawloop/demo_math.py.
• Expose clawloop demo math --dry-run through the installed CLI.
• Support python -m clawloop.demo_math --dry-run.
• Keep examples/demo_math.py as a thin shim for clone-based usage.
• Add tests for the CLI entry point.
• Add CI coverage that builds the wheel, installs it into a clean venv, and runs the installed demo.

Acceptance

• clawloop demo math --dry-run works from editable install.
• python -m clawloop.demo_math --dry-run works.
• python examples/demo_math.py --dry-run still works from a clone.
• CI validates the built wheel, not only editable installs.

[bordeauxred]

Codex review (2026-04-19) — expand artifact CI acceptance:

The job should validate more than just `clawloop demo math --dry-run`. Add to the wheel-install smoke step:

• `python -c "import clawloop; print(clawloop.version)"` — proves import works and version matches
• `python -m clawloop.demo_math --dry-run` — module entry point
• `clawloop --help` — proves CLI registers
• `clawloop demo math --dry-run` — flagship demo

Plus a content audit on the built artifacts before install:

• `tar -tzf dist/.tar.gz` and `unzip -l dist/.whl` should show no `benchmarks/`, `.codeboarding/`, `skyrl`, `runs/`, or local trace outputs

Also install from both wheel and sdist (sdist install exercises the full build path).