[dbrattli]

What changed

• Add a navigable guide for getting started, creating, filtering, transforming, combining, aggregating, error handling, time shifting, the reactive builder, and actor interoperability.
• Explain subscription ownership, builder ordering, actor output and terminal races, and the existing Fable compiler requirement in task-focused examples.
• Fix Reactive.retry so each subscription has its own retry budget and an exhausted budget forwards the source error. Keep Reactive.catch handling subsequent fallback errors as before.
• Add shared Scriptorium regressions for zero retries, the exact retry count, successful completion after a retry, and independent subscriber budgets.

Behavior and compatibility

The public signatures and dependencies are unchanged. retry n allows the initial attempt plus up to n retries. retry 0 and exhausted retry budgets now terminate with the source error instead of repeatedly handling it; subscribing again starts with a fresh budget.