fix(ci): add xdg-utils for ARM64 AppImage and suppress dead_code warnings

- Add xdg-utils dependency for xdg-mime binary required by AppImage bundler
- Remove unused McpStatus struct from gemini_mcp.rs (duplicate of claude_mcp.rs)
- Add #![allow(dead_code)] to proxy models reserved for future type-safe API

.github/workflows/release.yml

@@ -59,7 +59,8 @@ jobs:
             rpm \
             flatpak \
             flatpak-builder \
-            elfutils
+            elfutils \
+            xdg-utils
           # GTK/GLib stack for gdk-3.0, glib-2.0, gio-2.0
           sudo apt-get install -y --no-install-recommends \
             libgtk-3-dev \