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/assets/icons/mic_off.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="1em" height="1em" viewBox="0 0 24 24"><path fill="currentColor" d="M17.75 14.95L16.3 13.5q.35-.575.525-1.2T17 11h2q0 1.1-.325 2.088t-.925 1.862m-2.95-3L9 6.15V5q0-1.25.875-2.125T12 2t2.125.875T15 5v6q0 .275-.062.5t-.138.45M11 21v-3.1q-2.6-.35-4.3-2.312T5 11h2q0 2.075 1.463 3.538T12 16q.85 0 1.613-.262T15 15l1.425 1.425q-.725.575-1.588.963T13 17.9V21zm8.8 1.6L1.4 4.2l1.4-1.4l18.4 18.4z"/></svg>