Scaffold Spring Boot 4.0.5 project with domain packages

Maven project with Java 21. Dependencies: web, data-jpa, security,
validation, flyway, postgresql, springdoc-openapi 3.0.2.
Package-by-domain structure: auth, household, recipe, planning,
shopping, pantry, admin, common. JPA open-in-view disabled,
Hibernate ddl-auto=validate (Flyway owns the schema).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/.gitignore

@@ -0,0 +1,33 @@
+HELP.md
+target/
+.mvn/wrapper/maven-wrapper.jar
+!**/src/main/**/target/
+!**/src/test/**/target/
+
+### STS ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+
+### IntelliJ IDEA ###
+.idea
+*.iws
+*.iml
+*.ipr
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+build/
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### VS Code ###
+.vscode/