Spec: Upgrade Java Baseline to 24

[ganesh47]

Spec ID: java24.upgrade
File: /home/ganesh/projects/java-99-problems/specs/java-99-java24-upgrade.feature.md

Links:

• ADR: ADR: java24.upgrade #86
• Wiki: https://github.com/ganesh47/java-99-problems/wiki/Spec-Upgrade-Java-Baseline-to-24

Phases:

• Idea/Todo
• ADR/Design Review
• Plan
• Tasks
• Implementation
• Release
• Close

Features:

• toolchain.java24 (accept: pom.xml defines java.version=24 and compiler config consumes the property; PMD targetJdk is pinned to the highest supported level with rationale noted; mvnw verify defaults to Java 24 when no -Djava.version override is supplied)
• ci.java24 (accept: CI builds include Java 24 and pass with -Djava.version=24; Java 24-specific skips (if any) are documented and keep checks green)
• examples.java24 (accept: Problem implementations and tests compile/run under Java 24 in CI)
• docs.release (accept: CHANGELOG.md contains a v0.2.0 entry for the Java 24 upgrade; Release workflow publishes v0.2.0 with coverage artifact and ADR/wiki links)
• spec.workflow (accept: Spec issue/ADR/wiki links created via specs sync and ADR approved before implementation; PR uses the spec template with issue/ADR/wiki links and required checks green)

[github-actions]

Released v0.2.0: https://github.com/ganesh47/java-99-problems/releases/v0.2.0\nChangelog updated, ADR discussion noted, wiki updated: https://github.com/ganesh47/java-99-problems/wiki/Spec-Upgrade-Java-Baseline-to-24