Right-click or chevron-click on the sidebar strip's AI button now opens
a borderless overlay instead of a plain native menu: enabled engines
are listed with their bundled icons, the current engine is highlighted
with the acid accent + check, and a settings row at the bottom jumps
to Search settings. Clicking an engine selects it as the default and
opens it in the left panel in one click.
Bundled engine icons gained an svg-first fallback: engine-icons/<id>.svg
is picked up before <id>.png so plain color-coded letter tiles ship
alongside the existing bitmap favicons. Added tiles for ChatGPT, Grok,
Gemini and Phind — each a simple initial-on-color mark.
