docs(web-views): document how browser view events are delivered

[Klo1337]

The client contract declares the Browser*Event payload interfaces (BrowserInputFocusChangeEvent, BrowserCursorChangeEvent, BrowserResourceBlockedEvent, …), but they are not in EventMap and Web.on does not receive them, so the reference gives no way to find out how to subscribe.

Verified on a live server (build 1.0.0-3a40a8f): they are dispatched to the shared Events.on table under camelCase names derived from the payload interface (browserInputFocusChange, browserCursorChange), with the payload object as a single argument; a parallel Web.on(viewId, ...) subscription with the same names never fires.

This adds a short subsection to the web-views guide, right after the paragraph that points at the payload family in the client reference: the delivery channel, the viewId filtering caveat, and the main practical use (browserInputFocusChange as the reliable hotkey gate while typing into a page).

Rebased onto the reorganised guides (the original change targeted guides/events.md, which has since become guides/concepts/events.md; the web-views guide is the better home now that it exists).