feat(go): M6.2 — adults page (table, filters, credits/debts/unmatched, Pay buttons)

- Extract AssembleAdults(ctx) from ServeAdults so HTML and JSON API share one reconcile path.
- HTMLHandler gains *api.Handler; ServeAdults loads real data and renders adults.tmpl.
- AdultsPageData view model + qrHref/qrHrefAll funcMap (URL-encode /qr params, YYYY-MM→MM/YYYY).
- adults.tmpl: full reconcile table, per-cell status classes + cell-unpaid-current, Pay button hrefs,
  totals row, credits/debts/unmatched sections, filter controls, sheet links.
- static/js/filters.js: NFD-normalize name filter + month-range column hiding; future months hidden by default.
- TestAdultsPage asserts member name and cell text against fixture data.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

go/internal/web/api/handler.go

@@ -34,14 +34,23 @@ func (h *Handler) ServeVersion(w http.ResponseWriter, r *http.Request) {
 
 // ServeAdults handles GET /api/adults.
 func (h *Handler) ServeAdults(w http.ResponseWriter, r *http.Request) {
-	ctx := r.Context()
-	members, sortedMonths, txns, exceptions, err := h.loadAll(ctx, true)
+	resp, err := h.AssembleAdults(r.Context())
 	if err != nil {
 		h.writeError(w, r, err)
 		return
 	}
+	writeJSON(w, resp)
+}
+
+// AssembleAdults loads all data and builds the adults view model.
+// Shared between the JSON API route and the HTML handler.
+func (h *Handler) AssembleAdults(ctx context.Context) (AdultsResponse, error) {
+	members, sortedMonths, txns, exceptions, err := h.loadAll(ctx, true)
+	if err != nil {
+		return AdultsResponse{}, err
+	}
 	result := domreconcile.Reconcile(members, sortedMonths, txns, exceptions, time.Now().Year())
-	writeJSON(w, buildAdultsResponse(members, sortedMonths, result, txns, h.Config, time.Now().Format("2006-01")))
+	return buildAdultsResponse(members, sortedMonths, result, txns, h.Config, time.Now().Format("2006-01")), nil
 }
 
 // ServeJuniors handles GET /api/juniors.