Integrate G15 submodules with Debian 13 packaging and devcontainer

packaging/overlays/v1/g15macro-build.patch

@@ -0,0 +1,19 @@
+Description: Fix legacy build include switch and implicit-int declaration
+Author: G15 packaging contributors
+Forwarded: not-needed
+Last-Update: 2026-09-07
+--- a/Makefile.am
++++ b/Makefile.am
+@@ -11,7 +11,6 @@
+ image_DATA = ${top_builddir}/g15macro.wbmp
+ 
+ LIBS = -Wl,--no-add-needed -lg15daemon_client -lg15render -lX11 -lXtst -lpthread
+-IMCLUDES = -I
+ g15macro_SOURCES =  g15macro.c
+ 
+ 
+--- a/g15macro.c
++++ b/g15macro.c
+@@ -191,1 +191,1 @@
+-int map_gkey(keystate){
++int map_gkey(int keystate){