Publish a docs site; set the repo description and topics

[btravers]

From the 2026-08-13 repo audit.

start is the least discoverable repo in the org:

• No VitePress docs site — the only library repo without one, while unthrown, amqp-contract and temporal-contract all publish theirs with the shared @btravstack/theme.
• No GitHub repo description and no topics.

For the framework ambition, start is the front door — it should be the most visible repo, not the least. The four READMEs (1,516 lines including the runtime packages) are already docs-shaped; the root README's sections map directly onto a docs-site structure, and packages/start's samples are already compile-gated by docs-examples.test-d.ts.

Acceptance

• A VitePress site on the shared theme, published like the sibling repos.
• Repo description and topics set.