chore: update gitignore files

Agrega prompts/ al gitignore raiz. Actualiza dag_engine/.gitignore
con patrones estandar para Go, frontend y editor.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

@@ -55,3 +55,4 @@ Thumbs.db
 
 broken_paths.txt
 imgui.ini
+prompts/

apps/dag_engine/.gitignore

@@ -1,5 +1,18 @@
-dag-engine
+# Build output
 dag_engine
-dag_engine.db
-frontend/node_modules/
+*.exe
+
+# Frontend build
 frontend/dist/
+frontend/node_modules/
+
+# Go
+vendor/
+
+# Editor
+.idea/
+.vscode/
+*.swp
+
+# OS
+.DS_Store