Migrate build/runtime baseline to Java 25 and align CI/docs

[Copilot]

This updates the service from Java 11 to Java 25 end-to-end so the project compiles, runs, and documents against the new baseline. It also applies selective Java language modernizations in touched service/resource paths.

• Build + toolchain baseline

  • Set Maven Java properties to 25 (source, target, release).
  • Updated compiler/test plugins to Java-25-compatible versions (maven-compiler-plugin 3.15.0, surefire/failsafe 3.5.6).
  • Consolidated repeated test JVM module-open args into a shared Maven property for consistency.

• CI runtime alignment

  • Switched GitHub Actions Java setup from JDK 11 to JDK 25.

• Source-level modernization (Java 25-capable syntax)

  • Replaced legacy type-check/cast branches with pattern matching in WizardService.
  • Converted house-description switch to a switch expression.
  • Adopted unnamed catch variable where exception binding is unused.

• Developer documentation

  • Updated README tech-stack/prerequisite references from Java 11 to Java 25.

// before
if (event instanceof Wizard) {
    Wizard w = (Wizard) event;
    return "Wizard registration: " + w.getFirstName() + " " + w.getLastName();
}

// after
if (event instanceof Wizard w) {
    return "Wizard registration: " + w.getFirstName() + " " + w.getLastName();
}