JasperReports 6.19.1→7.0.3

Spike: Assess migration impact for JasperReports 7.0.3

Goal: Identify breaking changes from 6.19.1→7.0.3; list required code changes and risks.

Acceptance criteria:
- Document with checklist of impacted classes/methods
- Document build/toolchain needs
- Provide a migration plan
- Only accept if all existing tests pass 100%

Assignee: Copilot
Labels: enhancement

Parent issue: #114