Add blitz feature for Dioxus Native rendering support

Add an orthogonal `blitz` feature flag that switches the rendering
framework from dioxus webview to dioxus-native (Blitz). Can be combined
with `desktop` or `mobile` features. Also bumps rfd to ^0.17.0 (upstream
git moved forward), removes stale gui-level [patch.crates-io] section,
and adds xdotool to the Dockerfile for libxdo (blitz-shell dependency).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

gui/src/lib.rs

@@ -5,6 +5,9 @@ use app::STATE;
 use asynchronous_codec::FramedRead;
 use asynchronous_codec::FramedWrite;
 use color_eyre::eyre::{bail, Error};
+#[cfg(feature = "blitz")]
+use dioxus_native::prelude::*;
+#[cfg(not(feature = "blitz"))]
 use dioxus::prelude::*;
 use futures::select;
 use futures::AsyncRead;