Pull 350+ lines of inline per-row computation out of adults_view,
juniors_view, and payments into three pure builder functions with no
Flask globals or IO dependencies. Route handlers now contain only
cache/IO calls and a single render_template. No behaviour change —
all 27 tests pass.
Also moves get_month_labels, group_payments_by_person, and
adapt_junior_members out of app.py. Prep for /api/* shadow endpoints
(M5 Go parity).
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
