Four new JSON routes mirror the Go /api/* handlers so the M5.4 parity
tool can diff them: /api/version, /api/adults, /api/juniors,
/api/payments. A small _unwrap_view_model_for_api() helper in app.py
expands the three pre-serialised JSON strings in the view-model dicts
and renames month_labels_json → month_labels and
raw_payments_json → raw_payments to match the Go wire contract.
Tests in test_app.py assert top-level key sets match the Go API schema
and that member_data, month_labels, raw_payments are objects not strings.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
