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/domain/reconcile/reconcile.go

@@ -20,10 +20,13 @@ type Exception struct {
 	Note   string
 }
 
-// FeeData holds the expected fee and attendance count for one member in one month.
+// FeeData holds the expected fee and attendance data for one member in one month.
 type FeeData struct {
-	Expected   int
-	Attendance int
+	Expected         int
+	IsUnknown        bool // true when junior has exactly 1 session (manual review; Python sentinel "?")
+	Attendance       int
+	JuniorAttendance int // junior-tab sessions; used for the :NJ,MA breakdown in the juniors view
+	AdultAttendance  int // adult-tab sessions for J-tier members; used for the :NJ,MA breakdown
 }
 
 // Member is one row from the attendance sheet.
@@ -39,11 +42,15 @@ type Member struct {
 type Transaction struct {
 	Date           string
 	Amount         float64
+	ManualFix      string   // "manual fix" column; non-empty disables re-inference
 	Person         string   // comma-separated canonical names (empty → use inference)
 	Purpose        string   // comma-separated "YYYY-MM" or "other:…" (empty → use inference)
 	InferredAmount *float64 // nil → fall back to Amount
 	Sender         string
+	VS             string // Variabilní symbol (Czech variable payment symbol)
 	Message        string
+	BankID         string
+	SyncID         string
 	UserID         string
 }
 
@@ -69,8 +76,11 @@ type OtherEntry struct {
 // MonthData is the ledger state for one member in one month.
 type MonthData struct {
 	Expected         int
+	IsUnknown        bool // mirrors FeeData.IsUnknown; not overridden by exceptions
 	OriginalExpected int
 	AttendanceCount  int
+	JuniorAttendance int // junior-tab sessions; for :NJ,MA breakdown in juniors view
+	AdultAttendance  int // adult-tab sessions; for :NJ,MA breakdown
 	Exception        *Exception
 	Paid             float64
 	Transactions     []TxEntry
@@ -173,8 +183,11 @@ func Reconcile(
 
 			ledger[name][m] = MonthData{
 				Expected:         expected,
+				IsUnknown:        fd.IsUnknown,
 				OriginalExpected: originalExpected,
 				AttendanceCount:  attendanceCount,
+				JuniorAttendance: fd.JuniorAttendance,
+				AdultAttendance:  fd.AdultAttendance,
 				Exception:        exInfo,
 				Paid:             0,
 				Transactions:     []TxEntry{},