v0.1.0-rc4 — bundle demo dataset + dynamic __version__

Patch on top of rc3 fixing two release-blocker bugs discovered by fresh-venv install verification.

What's fixed since rc3

• `memexa demo` no longer fails with `ModuleNotFoundError: No module named 'examples.demo_dataset'`. The pyproject wheel-include rule now bundles `examples/demo_dataset/` (the ingest module + 6 source JSON/JSONL files).
• `memexa version` now reports `0.1.0rc4` instead of the stale `0.1.0a0`. The version is read dynamically from installed-package metadata so it cannot drift again.

Both bugs were caused by configurations that worked in editable / source-tree installs but failed in fresh-wheel installs from PyPI — the exact scenario every new memexa user encounters. The internal release pre-flight checklist now requires a fresh-venv wheel install + run smoke test as Item 7.

Recommended install

```bash
pip install --pre memexa==0.1.0rc4
memexa demo # 30-second onboarding
memexa version # → memexa 0.1.0rc4
```

rc3 disposition

rc3 remains on PyPI (cannot be deleted). `pip install --pre memexa` resolves to rc4 automatically. Direct `pip install memexa==0.1.0rc3` still installs rc3 with the broken `memexa demo` — please use rc4.

Other content

All v0.1.0-rc3 content (agent-first brand consolidation, `--json` mode, 3-tier quickstart, docs/why.md + docs/cost.md) is included unchanged. See v0.1.0-rc3 release notes for the feature list.

Pull request: #16.

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