feat(go): M5.2 — HTTP handlers for /api/adults, /api/juniors, /api/payments, /api/version

- Add web/api/handler.go: Handler struct wiring Sources+Config into ServeAdults,
  ServeJuniors, ServePayments, ServeVersion
- Add web/api/build_common.go: getMonthLabels, groupRawPaymentsByPerson, settledBalance,
  domain-to-wire converters, ensureSlice generic helper
- Add web/api/build_adults.go: buildAdultsResponse + buildAdultMemberRow mirroring
  scripts/views.py:build_adults_view_model
- Add web/api/build_juniors.go: buildJuniorsResponse + buildJuniorMemberRow mirroring
  scripts/views.py:build_juniors_view_model, including "?" sentinel and :NJ,MA breakdown
- Add web/api/build_payments.go: buildPaymentsResponse with Unmatched/Unknown bucket
- Extend reconcile.FeeData/MonthData with IsUnknown, JuniorAttendance, AdultAttendance
- Extend reconcile.Transaction with ManualFix, VS, BankID, SyncID for raw_payments wire field
- Export membership.AdultMergedMonths and JuniorMergedMonths
- Update sources.go to propagate new FeeData fields and parse extra transaction columns
- Wire sources+cfg into web.Run; register /api/* routes via Go 1.22 method+path patterns
- Fix pre-existing gofumpt formatting in fio_test.go and fio_table.go

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

go/internal/web/api/build_common.go

@@ -0,0 +1,184 @@
+package api
+
+import (
+	"fuj-management/go/internal/domain/czech"
+	"regexp"
+	"sort"
+	"strings"
+	"time"
+
+	domreconcile "fuj-management/go/internal/domain/reconcile"
+)
+
+// getMonthLabels builds display labels for sortedMonths, merging month names
+// (e.g. "Dec+Jan 2026") when mergedMonths maps a source month into this target.
+// Mirrors scripts/views.py:get_month_labels.
+func getMonthLabels(sortedMonths []string, mergedMonths map[string]string) map[string]string {
+	labels := make(map[string]string, len(sortedMonths))
+	for _, m := range sortedMonths {
+		dt, err := time.Parse("2006-01", m)
+		if err != nil {
+			labels[m] = m
+			continue
+		}
+		var mergedIn []string
+		for src, dst := range mergedMonths {
+			if dst == m {
+				mergedIn = append(mergedIn, src)
+			}
+		}
+		sort.Strings(mergedIn)
+		if len(mergedIn) == 0 {
+			labels[m] = dt.Format("Jan 2006")
+			continue
+		}
+		allMonths := append(mergedIn, m) //nolint:gocritic // intentional: mergedIn already owned
+		sort.Strings(allMonths)
+		years := map[int]bool{}
+		for _, x := range allMonths {
+			if d, err2 := time.Parse("2006-01", x); err2 == nil {
+				years[d.Year()] = true
+			}
+		}
+		parts := make([]string, 0, len(allMonths))
+		if len(years) > 1 {
+			for _, x := range allMonths {
+				if d, err2 := time.Parse("2006-01", x); err2 == nil {
+					parts = append(parts, d.Format("Jan 2006"))
+				}
+			}
+			labels[m] = strings.Join(parts, "+")
+		} else {
+			for _, x := range allMonths {
+				if d, err2 := time.Parse("2006-01", x); err2 == nil {
+					parts = append(parts, d.Format("Jan"))
+				}
+			}
+			labels[m] = strings.Join(parts, "+") + " " + dt.Format("2006")
+		}
+	}
+	return labels
+}
+
+// labelsForMonths returns the display labels for sortedMonths in slice order.
+func labelsForMonths(sortedMonths []string, labels map[string]string) []string {
+	out := make([]string, len(sortedMonths))
+	for i, m := range sortedMonths {
+		out[i] = labels[m]
+	}
+	return out
+}
+
+var questionMarkRe = regexp.MustCompile(`\[\?\]\s*`)
+
+// canonicalKey returns a normalized form of a person name used for deduplication.
+// Mirrors scripts/match_payments.py:canonical_member_key.
+func canonicalKey(name string) string {
+	return strings.Join(strings.Fields(czech.Normalize(name)), " ")
+}
+
+// groupRawPaymentsByPerson groups transactions by the "person" column,
+// canonicalizing names against memberNames where possible.
+// Mirrors scripts/views.py:group_payments_by_person (without the
+// "Unmatched / Unknown" bucket that is payments-view-specific).
+func groupRawPaymentsByPerson(txns []domreconcile.Transaction, memberNames []string) map[string][]RawTransaction {
+	canonicalByKey := make(map[string]string, len(memberNames))
+	for _, n := range memberNames {
+		k := canonicalKey(n)
+		if _, exists := canonicalByKey[k]; !exists {
+			canonicalByKey[k] = n
+		}
+	}
+	grouped := make(map[string][]RawTransaction)
+	for _, tx := range txns {
+		person := strings.TrimSpace(tx.Person)
+		if person == "" {
+			continue
+		}
+		for _, p := range strings.Split(person, ",") {
+			p = questionMarkRe.ReplaceAllString(p, "")
+			p = strings.TrimSpace(p)
+			if p == "" {
+				continue
+			}
+			key := p
+			if canonical, ok := canonicalByKey[canonicalKey(p)]; ok {
+				key = canonical
+			}
+			grouped[key] = append(grouped[key], rawTxFromDomain(tx))
+		}
+	}
+	for k := range grouped {
+		sort.Slice(grouped[k], func(i, j int) bool {
+			return grouped[k][i].Date > grouped[k][j].Date
+		})
+	}
+	return grouped
+}
+
+// rawTxFromDomain converts a domain Transaction to the wire RawTransaction.
+func rawTxFromDomain(tx domreconcile.Transaction) RawTransaction {
+	inferredAmount := 0.0
+	if tx.InferredAmount != nil {
+		inferredAmount = *tx.InferredAmount
+	}
+	return RawTransaction{
+		Date:           tx.Date,
+		Amount:         tx.Amount,
+		ManualFix:      tx.ManualFix,
+		Person:         tx.Person,
+		Purpose:        tx.Purpose,
+		InferredAmount: inferredAmount,
+		Sender:         tx.Sender,
+		VS:             tx.VS,
+		Message:        tx.Message,
+		BankID:         tx.BankID,
+		SyncID:         tx.SyncID,
+	}
+}
+
+// memberTxFromDomain converts a domain TxEntry to a wire MemberTxEntry.
+func memberTxFromDomain(te domreconcile.TxEntry) MemberTxEntry {
+	return MemberTxEntry{
+		Amount:     te.Amount,
+		Date:       te.Date,
+		Sender:     te.Sender,
+		Message:    te.Message,
+		Confidence: te.Confidence,
+	}
+}
+
+// memberOtherFromDomain converts a domain OtherEntry to a wire MemberOtherEntry.
+func memberOtherFromDomain(oe domreconcile.OtherEntry) MemberOtherEntry {
+	return MemberOtherEntry{
+		Amount:     oe.Amount,
+		Date:       oe.Date,
+		Sender:     oe.Sender,
+		Message:    oe.Message,
+		Purpose:    oe.Purpose,
+		Confidence: oe.Confidence,
+	}
+}
+
+// settledBalance computes the settled balance: sum of (paid − expected) for months
+// strictly before currentMonth. Months with IsUnknown=true are excluded to match
+// Python's isinstance(exp, int) guard (skips "?" months).
+func settledBalance(mr domreconcile.MemberResult, currentMonth string) int {
+	total := 0
+	for m, md := range mr.Months {
+		if m >= currentMonth || md.IsUnknown {
+			continue
+		}
+		total += int(md.Paid) - md.Expected
+	}
+	return total
+}
+
+// ensureSlice returns s unchanged when non-nil, or an empty (non-nil) slice so
+// json.Marshal emits [] instead of null.
+func ensureSlice[T any](s []T) []T {
+	if s == nil {
+		return []T{}
+	}
+	return s
+}