chore: update gitignore and add config files

- Add frontend/dist and backend/dist to gitignore
- Remove build artifacts from tracking
- Add .dockerignore and .env.example

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

.gitignore

@@ -4,6 +4,8 @@ node_modules/
 # Build output
 dist/
 build/
+frontend/dist/
+backend/dist/
 
 # Environment files
 .env