scaffold: React 19 + Spring Boot 3.4 + PostgreSQL project

Sets up toolchain pinning, format/lint (Biome + Spotless), lefthook
pre-commit hooks, Docker Compose for Postgres, and trivial passing
tests for both stacks.

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

backend/.mvn/wrapper/maven-wrapper.properties

@@ -0,0 +1,2 @@
+distributionUrl=https://repo.maven.apache.org/maven2/org/apache/maven/apache-maven/3.9.9/apache-maven-3.9.9-bin.tar.gz
+wrapperVersion=3.3.2

backend/mvnw

@@ -0,0 +1,30 @@
+#!/bin/sh
+# Minimal Maven Wrapper — downloads Apache Maven on first run and caches it.
+set -e
+
+MAVEN_VERSION="3.9.9"
+MAVEN_CACHE="${HOME}/.m2/wrapper/dists/apache-maven-${MAVEN_VERSION}"
+MAVEN_URL="https://repo.maven.apache.org/maven2/org/apache/maven/apache-maven/${MAVEN_VERSION}/apache-maven-${MAVEN_VERSION}-bin.tar.gz"
+
+if [ ! -f "${MAVEN_CACHE}/bin/mvn" ]; then
+  MAVEN_TMP="${MAVEN_CACHE}.tmp.$$"
+  if mkdir "${MAVEN_CACHE}.lock" 2>/dev/null; then
+    echo "Downloading Apache Maven ${MAVEN_VERSION}..." >&2
+    mkdir -p "${MAVEN_TMP}"
+    if command -v curl > /dev/null 2>&1; then
+      curl -fsSL "${MAVEN_URL}" | tar -xz --strip-components=1 -C "${MAVEN_TMP}"
+    elif command -v wget > /dev/null 2>&1; then
+      wget -qO- "${MAVEN_URL}" | tar -xz --strip-components=1 -C "${MAVEN_TMP}"
+    else
+      rm -rf "${MAVEN_TMP}" "${MAVEN_CACHE}.lock"
+      echo "ERROR: curl or wget is required to download Maven" >&2
+      exit 1
+    fi
+    mv "${MAVEN_TMP}" "${MAVEN_CACHE}"
+    rm -rf "${MAVEN_CACHE}.lock"
+  else
+    while [ -d "${MAVEN_CACHE}.lock" ]; do sleep 0.2; done
+  fi
+fi
+
+exec "${MAVEN_CACHE}/bin/mvn" "$@"

backend/pom.xml

@@ -0,0 +1,87 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>org.springframework.boot</groupId>
+        <artifactId>spring-boot-starter-parent</artifactId>
+        <version>3.4.0</version>
+        <relativePath/>
+    </parent>
+
+    <groupId>com.example</groupId>
+    <artifactId>app</artifactId>
+    <version>0.0.1-SNAPSHOT</version>
+    <name>app</name>
+
+    <properties>
+        <java.version>21</java.version>
+    </properties>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-web</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-data-jpa</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-validation</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.flywaydb</groupId>
+            <artifactId>flyway-core</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.flywaydb</groupId>
+            <artifactId>flyway-database-postgresql</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.postgresql</groupId>
+            <artifactId>postgresql</artifactId>
+            <scope>runtime</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-test</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <configuration>
+                    <compilerArgs>
+                        <arg>-Xlint:all</arg>
+                        <arg>-Xlint:-processing</arg>
+                        <arg>-Xlint:-serial</arg>
+                    </compilerArgs>
+                </configuration>
+            </plugin>
+            <plugin>
+                <groupId>com.diffplug.spotless</groupId>
+                <artifactId>spotless-maven-plugin</artifactId>
+                <version>2.44.0</version>
+                <configuration>
+                    <java>
+                        <googleJavaFormat>
+                            <version>1.23.0</version>
+                            <style>GOOGLE</style>
+                        </googleJavaFormat>
+                        <removeUnusedImports/>
+                        <trimTrailingWhitespace/>
+                        <endWithNewline/>
+                    </java>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+</project>

backend/src/main/java/com/example/app/Application.java

@@ -0,0 +1,11 @@
+package com.example.app;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class Application {
+  public static void main(String[] args) {
+    SpringApplication.run(Application.class, args);
+  }
+}

backend/src/main/resources/application.yml

@@ -0,0 +1,17 @@
+spring:
+  application:
+    name: app
+  datasource:
+    url: ${DATABASE_URL:jdbc:postgresql://localhost:5432/app_dev}
+    username: ${DATABASE_USERNAME:app}
+    password: ${DATABASE_PASSWORD:app}
+  jpa:
+    hibernate:
+      ddl-auto: validate
+    open-in-view: false
+  flyway:
+    enabled: true
+
+logging:
+  level:
+    root: ${LOG_LEVEL:INFO}

backend/src/test/java/com/example/app/ApplicationTest.java

@@ -0,0 +1,12 @@
+package com.example.app;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.Test;
+
+class ApplicationTest {
+  @Test
+  void applicationClassLoads() {
+    assertThat(Application.class.getSimpleName()).isEqualTo("Application");
+  }
+}