Adds a two-step new thread modal: step one picks mode, step two
configures aspect ratio (Art mode only, six options) and resolution
(all modes: 1K/2K/4K). Settings are stored on the thread and forwarded
to the Gemini API on every send, retry, and edit. Also regenerates
icon.ico with Python to produce a clean all-BMP ICO compatible with
both Tauri's proc macro and llvm-rc cross-compilation.
hikari
