Synthesize an extra AutocompleteSuggestion at the top of the Search
Suggestions section whenever there is a configured search engine and
the typed query is not URL-shaped.
Use the query as the row's primary text, carry a "Search with <engine>"
subtitle, and render that subtitle in the AppKit and Qt popups so the
explicit search fallback stays visible and readable even when history
fills the list.
Replace the old QCompleter-based popup with a custom list that renders
AutocompleteSuggestion rows with titles/URLs/section headers/favicons.
Parent the popup inside the window so it does not steal focus, route
keyboard and mouse activation through WebView::Autocomplete, and add
inline completion with backspace suppression and top-row selection.
