feat: add warning popup if existing desktop process is present

programs/GNUmakefile

@@ -216,8 +216,8 @@ login: bearssl libc
 shell:
 	$(MAKE) -C src/shell
 
-# Build desktop via its own Makefile (depends on libc, libjpeg, and bearssl for user.h).
-desktop: libc libjpeg bearssl
+# Build desktop via its own Makefile (depends on libc, libjpeg, bearssl for user.h, and dialogs for duplicate-session warnings).
+desktop: libc libjpeg bearssl libloader dialogs
 	$(MAKE) -C src/desktop
 
 # Copy SVG icons for the desktop into bin/icons/.