Package-level declarations

A PageBehaviour simulating a browser running datastar: it maintains a signal store, evaluates data-* expressions, applies datastar-patch-elements/patch-signals SSE events to the live document, and sends non-local signals with every backend action.

A headless, pure-Kotlin approximation of a browser running datastar v1: an Http4kWebDriver with a DatastarBehaviour plugged in, so navigation, history and cookies all work as standard.