Fixed HTML navbar scrolls with content in Normal Mode #41

When using a fixed-position HTML navbar (e.g., position: fixed; top: 0) in Normal Mode with edge-to-edge enabled, the navbar scrolls with the page content instead of staying pinned to the top.

This happens because contentInsetAdjustmentBehavior = .never on the WKWebView means the scroll view doesn't account for fixed elements in the same way a native navigation bar would.

To reproduce:

1. Create a Normal Mode app with a fixed HTML navbar (no native navbar)
2. Add enough content to scroll
3. Scroll down — the fixed navbar moves with the content

Visible in: Habits demo app

Workaround: Use a native navbar (native_navbar_tag) instead of an HTML fixed navbar.