feat: add Dioxus and GPUI UI prototypes for framework comparison
Dioxus (ui-dioxus/): 2,169 lines, WebView mode (same wry as Tauri),
Catppuccin theme, 12 components, agor-core integration, compiles clean.
Evolution path — keeps xterm.js, gradual migration from Tauri.
GPUI (ui-gpui/): 2,490 lines, GPU-accelerated rendering, alacritty_terminal
for native terminal, 17 files, Catppuccin palette, demo data.
Revolution path — pure Rust UI, 120fps target, no WebView.
Both are standalone (not in workspace), share agor-core backend.
Created for side-by-side comparison to inform framework decision.
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