Support side navigation bars in Web projects

Allow a WebPage's Navigation Bar to appear at the top, on the left, or on the right of its content.

Side navigation should offer a configurable width, vertically arranged items with symbols, expandable groups, and a clear current-page indicator. On smaller screens it should switch to a dismissible side drawer so the page remains usable.

Developers should continue to design a reusable Navigation Bar once, assign it to pages, and use its existing WebPage destinations, URL links, and shared action handlers. Each page chooses its placement and keeps its own selection and runtime state. Existing top navigation should retain its current behaviour.