Add consumer compatibility CI across supported JDKs and all published JARs

Follow-up to #90 (reviewed at 31588e1). This tracks work intentionally kept separate from the modernization PR.

Why

The checked-in CI builds and tests on JDK 17 only. #90 adds packaged-core OSGi R6 and module-discovery tests, but equivalent coverage for all four artifacts and actual Java 8 runtime compatibility remains incomplete.

The review checked core consumer execution on JDK 11/17/21/25 and Java 8 class-file versions; it did not execute on Java 8. Past issues #79 and #81 demonstrate why compilation and ordinary unit tests alone are insufficient.

Acceptance criteria

• Build artifacts with the supported build JDK, then run separate consumer tests on the supported runtime matrix, including an actual Java 8 runtime. Do not attempt to run the modern build toolchain or incompatible test-app dependencies on Java 8.
• Document runtime support per artifact and use appropriate servlet/JSP/ESAPI dependency versions in each fixture.
• Exercise classpath, explicit JPMS, automatic-module fallback, and legacy/current OSGi consumption where applicable; include real encoding/tag/adapter calls.
• Add artifact-level assertions for all four JARs: automatic module names, explicit descriptors, OSGi identities/imports/exports, multi-release layout, bytecode/API baseline, TLD resources, and absence of test dependencies in published runtime contents.
• Keep consumers isolated from reactor test classpaths so missing packaged classes or dependencies cannot be masked.
• Keep the Docker/Selenium test app on its own compatible JDK/container job and keep failure diagnostics available.
• Coordinate adapter module-path tests with the separate JPMS-readability fix; document known limitations rather than presenting descriptor discovery as successful adapter execution.

Preserve the intentionally different published automatic and explicit module names documented in #90.

Beginne mit dem Lesen von Issue #90 und der Überprüfung von Commit 31588e1; untersuche anschließend die eingecheckte CI und die bestehende Abdeckung paketierter Consumer. Ordne die vier veröffentlichten JARs der unterstützten JDK-Laufzeitmatrix, der Docker/Selenium-Testanwendung und den aufgeführten Classpath-, JPMS-, OSGi-, Bytecode-, Ressourcen- und Abhängigkeitsprüfungen zu. Als abgeschlossen gilt die Aufgabe, wenn isolierte Consumer-Jobs die Akzeptanzkriterien abdecken und bekannte Adapter-Einschränkungen dokumentieren.