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/server.go

@@ -33,7 +33,7 @@ func Run(logger *slog.Logger, addr string, build BuildInfo, sources membership.S
 		Config:       cfg,
 		Logger:       logger,
 	}
-	hh := NewHTMLHandler(renderer, build)
+	hh := NewHTMLHandler(renderer, build, ah)
 
 	staticSubFS, err := fs.Sub(staticFS, "static")
 	if err != nil {