Adds report_type support across the full stack:
- Backend: REPORT_TYPES mapping, fallgruppen filter in all 5 sheet
calculations, dynamic Excel columns, report_type DB column with
Alembic migration 007
- Frontend: report type dropdown in generation form, type column in
reports table, dynamic fallgruppen in ReportViewer
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>