fix desktop integration and rename Linux runner

StartupWMClass now matches the GTK application ID
(net.schweitz.clide) so the running window groups with the
launcher icon. Desktop file installs as
net.schweitz.clide.desktop per freedesktop convention.

Renamed my_application.{cc,h} to clide_app.{cc,h} with
matching GObject type (ClideApp / CLIDE_APP).

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

linux/runner/main.cc

@@ -1,6 +1,6 @@
-#include "my_application.h"
+#include "clide_app.h"
 
 int main(int argc, char** argv) {
-  g_autoptr(MyApplication) app = my_application_new();
+  g_autoptr(ClideApp) app = clide_app_new();
   return g_application_run(G_APPLICATION(app), argc, argv);
 }