refactor: move Python implementation to legacy/, make Go primary

Go (go/) becomes the primary implementation. The original Python
version moves to legacy/ and is kept runnable; new features are still
built in both (see the Dual implementation rule in CLAUDE.md).

- git mv app.py, scripts/, templates/, tests/, pyproject.toml, uv.lock
  and build/ into legacy/
- Makefile: Python targets point at legacy/, venv in legacy/.venv,
  CREDENTIALS_PATH exported for the root .secret/ file
- CI and make image build the Python image with legacy/ as context;
  the Makefile is no longer copied into the image
- legacy/.dockerignore moved to the context root so it takes effect
- CLAUDE.md, docs/README.md, Go comments, fixture README, capture
  script and VS Code launch config updated to the new layout

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

go/internal/services/banksync/infer.go

@@ -30,7 +30,7 @@ type sheetReadWriter interface {
 // InferPayments fills empty Person/Purpose/Inferred Amount cells in the payments
 // sheet using name and month matching against the member list.
 // Returns the number of rows updated (or that would be updated on dry-run).
-// Ports scripts/infer_payments.py infer_payments.
+// Ports legacy/scripts/infer_payments.py infer_payments.
 func InferPayments(
 	ctx context.Context,
 	spreadsheetID string,

go/internal/services/banksync/sync.go

@@ -12,7 +12,7 @@ import (
 )
 
 // columnLabels is the canonical header for the payments sheet.
-// Mirrors COLUMN_LABELS in scripts/sync_fio_to_sheets.py.
+// Mirrors COLUMN_LABELS in legacy/scripts/sync_fio_to_sheets.py.
 var columnLabels = []string{
 	"Date", "Amount", "manual fix", "Person", "Purpose",
 	"Inferred Amount", "Sender", "VS", "Message", "Bank ID", "Sync ID",
@@ -37,7 +37,7 @@ type SyncOpts struct {
 
 // SyncToSheets fetches Fio transactions from all provided clients and appends
 // new ones to the payments sheet. Returns the number of rows appended.
-// Ports scripts/sync_fio_to_sheets.py sync_to_sheets.
+// Ports legacy/scripts/sync_fio_to_sheets.py sync_to_sheets.
 func SyncToSheets(
 	ctx context.Context,
 	spreadsheetID string,

go/internal/services/membership/format_fees.go

@@ -9,11 +9,11 @@ import (
 )
 
 // printFeesTable writes a fixed-width adult-fees table to w.
-// Mirrors scripts/calculate_fees.py main().
+// Mirrors legacy/scripts/calculate_fees.py main().
 //
 // Verify with:
 //
-//	PYTHONPATH=scripts:. python scripts/calculate_fees.py
+//	PYTHONPATH=legacy/scripts:legacy python legacy/scripts/calculate_fees.py
 func printFeesTable(w io.Writer, members []reconcile.Member, sortedMonths []string) {
 	type row struct {
 		name string

go/internal/services/membership/format_fees_test.go

@@ -1,8 +1,8 @@
 package membership
 
-// Golden strings verified against scripts/calculate_fees.py on 2026-05-06:
+// Golden strings verified against legacy/scripts/calculate_fees.py on 2026-05-06:
 //
-//	PYTHONPATH=scripts:. python scripts/calculate_fees.py
+//	PYTHONPATH=legacy/scripts:legacy python legacy/scripts/calculate_fees.py
 //
 // (feed equivalent fixture data via attendance sheet or local CSV)
 

go/internal/services/membership/format_reconcile.go

@@ -10,11 +10,11 @@ import (
 )
 
 // printReconcileReport writes the full balance report to w.
-// Mirrors scripts/match_payments.py print_report().
+// Mirrors legacy/scripts/match_payments.py print_report().
 //
 // Verify with:
 //
-//	PYTHONPATH=scripts:. python -c '
+//	PYTHONPATH=legacy/scripts:legacy python -c '
 //	from match_payments import print_report, reconcile, fetch_sheet_data, fetch_exceptions
 //	...'
 func printReconcileReport(w io.Writer, result reconcile.Result, sortedMonths []string) {

go/internal/services/membership/format_reconcile_test.go

@@ -1,8 +1,8 @@
 package membership
 
-// Golden strings verified against scripts/match_payments.py print_report() on 2026-05-06:
+// Golden strings verified against legacy/scripts/match_payments.py print_report() on 2026-05-06:
 //
-//	PYTHONPATH=scripts:. python -c '
+//	PYTHONPATH=legacy/scripts:legacy python -c '
 //	from match_payments import print_report
 //	result = {
 //	  "members": {

go/internal/services/membership/sources.go

@@ -18,20 +18,20 @@ import (
 	"time"
 )
 
-// Attendance CSV column indices (mirrors COL_* in scripts/attendance.py)
+// Attendance CSV column indices (mirrors COL_* in legacy/scripts/attendance.py)
 const (
 	colName      = 0
 	colTier      = 1
 	firstDateCol = 3
 )
 
-// AdultMergedMonths mirrors ADULT_MERGED_MONTHS in scripts/attendance.py.
+// AdultMergedMonths mirrors ADULT_MERGED_MONTHS in legacy/scripts/attendance.py.
 // Source month → target month (source attendance accumulated into target).
 var AdultMergedMonths = map[string]string{
 	"2025-09": "2025-10",
 }
 
-// JuniorMergedMonths mirrors JUNIOR_MERGED_MONTHS in scripts/attendance.py.
+// JuniorMergedMonths mirrors JUNIOR_MERGED_MONTHS in legacy/scripts/attendance.py.
 var JuniorMergedMonths = map[string]string{
 	"2025-12": "2026-01",
 	"2025-09": "2025-10",
@@ -127,11 +127,11 @@ func (s *realSources) LoadExceptions(ctx context.Context) (map[reconcile.Excepti
 }
 
 // ---------------------------------------------------------------------------
-// Attendance CSV parsing (ports scripts/attendance.py)
+// Attendance CSV parsing (ports legacy/scripts/attendance.py)
 // ---------------------------------------------------------------------------
 
 // parseDates returns (columnIndex, YYYY-MM) pairs for all date columns.
-// Ports scripts/attendance.py parse_dates + strftime("%Y-%m").
+// Ports legacy/scripts/attendance.py parse_dates + strftime("%Y-%m").
 func parseDates(header []string) []struct {
 	col   int
 	month string
@@ -200,7 +200,7 @@ func countTrue(row []string, cols []int) int {
 
 // parseAdultRows converts raw CSV rows to []reconcile.Member.
 // Includes all tiers; fee is 0 for non-A tiers (reconcile filters downstream).
-// Ports scripts/attendance.py get_members_with_fees.
+// Ports legacy/scripts/attendance.py get_members_with_fees.
 func parseAdultRows(rows [][]string) ([]reconcile.Member, []string, error) {
 	if len(rows) < 2 {
 		return nil, nil, nil
@@ -246,7 +246,7 @@ func parseAdultRows(rows [][]string) ([]reconcile.Member, []string, error) {
 
 // parseJuniorRows builds junior members by merging tier-J rows from the adult tab
 // with the junior sheet, then calling CalculateJuniorFee.
-// Ports scripts/attendance.py get_junior_members_with_fees.
+// Ports legacy/scripts/attendance.py get_junior_members_with_fees.
 func parseJuniorRows(adultRows, juniorRows [][]string) ([]reconcile.Member, []string, error) {
 	if len(adultRows) < 2 || len(juniorRows) < 2 {
 		return nil, nil, nil
@@ -362,7 +362,7 @@ func parseJuniorRows(adultRows, juniorRows [][]string) ([]reconcile.Member, []st
 }
 
 // ---------------------------------------------------------------------------
-// Payments sheet row parsing (ports scripts/match_payments.py fetch_sheet_data)
+// Payments sheet row parsing (ports legacy/scripts/match_payments.py fetch_sheet_data)
 // ---------------------------------------------------------------------------
 
 func parseTransactionRows(rows [][]any) ([]reconcile.Transaction, error) {
@@ -466,7 +466,7 @@ func parseFloat(v any) float64 {
 }
 
 // ---------------------------------------------------------------------------
-// Exceptions tab parsing (ports scripts/match_payments.py fetch_exceptions)
+// Exceptions tab parsing (ports legacy/scripts/match_payments.py fetch_exceptions)
 // ---------------------------------------------------------------------------
 
 func parseExceptionRows(rows [][]any) map[reconcile.ExceptionKey]reconcile.Exception {