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/html_handler.go

@@ -1,20 +1,35 @@
 package web
 
-import "net/http"
+import (
+	"fuj-management/go/internal/web/api"
+	"net/http"
+)
 
 // HTMLHandler serves the Go-native HTML frontend.
 type HTMLHandler struct {
-	renderer *Renderer
-	build    BuildInfo
+	renderer   *Renderer
+	build      BuildInfo
+	apiHandler *api.Handler
 }
 
 // NewHTMLHandler constructs an HTMLHandler.
-func NewHTMLHandler(r *Renderer, b BuildInfo) *HTMLHandler {
-	return &HTMLHandler{renderer: r, build: b}
+func NewHTMLHandler(r *Renderer, b BuildInfo, ah *api.Handler) *HTMLHandler {
+	return &HTMLHandler{renderer: r, build: b, apiHandler: ah}
 }
 
 func (h *HTMLHandler) ServeAdults(w http.ResponseWriter, r *http.Request) {
-	h.renderer.Render(w, "adults", PageData{Active: "adults", Build: h.build})
+	data, err := h.apiHandler.AssembleAdults(r.Context())
+	if err != nil {
+		h.renderer.Render(w, "adults", AdultsPageData{
+			PageData: PageData{Active: "adults", Build: h.build},
+			Error:    err.Error(),
+		})
+		return
+	}
+	h.renderer.Render(w, "adults", AdultsPageData{
+		PageData: PageData{Active: "adults", Build: h.build},
+		Data:     data,
+	})
 }
 
 func (h *HTMLHandler) ServeJuniors(w http.ResponseWriter, r *http.Request) {