Upgrade Java baseline to 24

[ganesh47]

Summary

• Spec issue: Spec: Upgrade Java Baseline to 24 #87
• ADR/design review discussion: ADR: java24.upgrade #86
• Wiki page for spec/ADR: https://github.com/ganesh47/java-99-problems/wiki/Spec-Upgrade-Java-Baseline-to-24

Required checks

• spec-kit templates refreshed (Fetched spec-kit template: templates/spec-template.md -> .specs/spec-kit/spec-template.md
  Fetched spec-kit template: templates/plan-template.md -> .specs/spec-kit/plan-template.md
  Fetched spec-kit template: templates/tasks-template.md -> .specs/spec-kit/tasks-template.md
  Fetched spec-kit template: spec-driven.md -> .specs/spec-kit/spec-driven.md
  spec-kit templates refreshed from github/spec-kit@main
  Found 2 spec file(s).
• java24.upgrade (5 feature(s))
• specs.java-99-bootstrap (5 feature(s)) or Fetched spec-kit template: templates/spec-template.md -> .specs/spec-kit/spec-template.md
  Fetched spec-kit template: templates/plan-template.md -> .specs/spec-kit/plan-template.md
  Fetched spec-kit template: templates/tasks-template.md -> .specs/spec-kit/tasks-template.md
  Fetched spec-kit template: spec-driven.md -> .specs/spec-kit/spec-driven.md
  Downloaded spec-kit templates from github/spec-kit@main to .specs/spec-kit)
• Spec-kit availability check passed (

spec-kit:check
node scripts/check-spec-kit.js

ok: spec-driven.md
ok: templates/spec-template.md
ok: templates/plan-template.md
ok: templates/tasks-template.md
spec-kit template availability check passed)

• Specs coverage run
• Example conformance run (if applicable)
• Security scans (Semgrep/OSV-Scanner/Gitleaks/Checkov) green
• ADR/design review approved before merge
• Issue and project status updated (Todo → In Progress → Done)