cmd/drover: replace MessageBox stub with Wails GUI (internal/gui.Run)

Bare 'drover' (and 'drover gui') no longer pop a Win32 MessageBox —
they hand off to internal/gui which mounts a real Wails window with
the Classic React variant. The old gui_windows.go / gui_other.go
files are removed; their job is now done by internal/gui/run.go.

Auto-update on startup is unchanged — still runs before gui.Run().

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -8,10 +8,11 @@
 *.out
 
 # Wails
-/internal/frontend/node_modules/
-/internal/frontend/dist/
-/internal/frontend/wailsjs/
+/internal/gui/frontend/node_modules/
+/internal/gui/frontend/dist/
 .wails/
+# wailsjs/ is generated, but we keep it tracked because we hand-write
+# bindings/App.js for the gui-package layout (see comment in that file)
 
 # IDE
 /.idea/