PR135 — Examples & fixtures

[vecipher]

Why: Provide always-working, deterministic examples for the viewer & console.

What
• Add clematis/examples/run_bundles/run_demo_bundle.json generated from a tiny demo.
• Add a short HOWTO in the examples directory.
• Ensure examples are used in smoke tests (no heavy deps).

Accept
• python -m clematis export-logs on the demo outputs exactly the committed bundle.
• Viewer loads the example bundle without any interaction.

Touch
clematis/examples/run_bundles/run_demo_bundle.json
clematis/examples/README_frontend.md
tests/frontend/test_example_bundle.py