chore: add sources dir and debug-service skill, make Coolify primary

sources/ holds gitignored upstream checkouts for debugging a service
against its real code; the debug-service skill walks through it. Coolify
is now the primary deployment target and Dokploy optional.

.gitignore

@@ -21,3 +21,7 @@ desktop.ini
 *.swp
 .idea/
 .vscode/
+
+# Upstream source checkouts for debugging; only the directory itself is kept
+sources/*
+!sources/.gitkeep