Upgrade build to Java 11 / Spring Boot 2.7.18 / Gradle 7.6.4

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Summary

Java 8 → 11 across both build systems, with the coordinated bumps needed for Java 11 support:

• pom.xml: java.version 1.8 → 11, spring-boot-starter-parent 2.0.2.RELEASE → 2.7.18. Also <packaging>pom</packaging> → jar — with pom packaging Maven never compiled src/main/java at all, so the build "passed" without exercising the sources or producing an artifact.
• build.gradle: sourceCompatibility/targetCompatibility → 11 plus options.release = 11 (enforces the Java 11 API surface on newer JDKs), spring-boot-gradle-plugin → 2.7.18, compile/testCompile → implementation/testImplementation, bootJar { baseName/version } → archiveBaseName/archiveVersion (old properties removed in Gradle 7/8). Added spring-boot-starter-jdbc, h2, and spring-boot-properties-migrator to match the pom — Application.java imports JdbcTemplate, so the Gradle build did not compile without them.
• gradle/wrapper/gradle-wrapper.properties: Gradle 4.6 → 7.6.4.
• gradlew/mvnw: made executable. README prerequisite updated to Java 11.

No Java source changes were needed. Verified on OpenJDK 11.0.32: ./gradlew clean build and mvn clean package both succeed and produce gs-spring-boot-0.1.0.jar. (./mvnw itself could not be verified here — its Maven 3.3.9 distribution download from repo1.maven.org was rate-limited with HTTP 429.)

Left untouched: the defunct gturnquist-quoters.cfapps.io call in Application.java (runtime-only, unrelated to the upgrade), and the tracked target/classes/*.class files.

Devin-Org: engineering

Link to Devin session: https://app.devin.ai/sessions/27eb2626eee7463397268bd04addb238
Open in Devin Desktop: https://app.devin.ai/desktop/session/27eb2626eee7463397268bd04addb238?variant=devin
Requested by: @bryce-h-t

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Devin Review found 4 potential issues.