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/tests/parity/pure/build_name_variants/build_name_variants_parity_test.go

@@ -13,7 +13,7 @@ import (
 
 // Verify expected values against live Python:
 //
-//	PYTHONPATH=scripts:. python3 -c "from match_payments import _build_name_variants; print(_build_name_variants('František Vrbík (Štrúdl)'))"
+//	PYTHONPATH=legacy/scripts:legacy python3 -c "from match_payments import _build_name_variants; print(_build_name_variants('František Vrbík (Štrúdl)'))"
 
 func TestBuildNameVariantsParity(t *testing.T) {
 	t.Parallel()

go/tests/parity/pure/calculate_fee/calculate_fee_parity_test.go

@@ -12,7 +12,7 @@ import (
 
 // Verify expected values against live Python:
 //
-//	PYTHONPATH=scripts:. python3 -c "from attendance import calculate_fee; print(calculate_fee(2, '2026-01'))"
+//	PYTHONPATH=legacy/scripts:legacy python3 -c "from attendance import calculate_fee; print(calculate_fee(2, '2026-01'))"
 
 func TestCalculateFeeParity(t *testing.T) {
 	t.Parallel()

go/tests/parity/pure/calculate_junior_fee/calculate_junior_fee_parity_test.go

@@ -12,7 +12,7 @@ import (
 
 // Verify expected values against live Python:
 //
-//	PYTHONPATH=scripts:. python3 -c "from attendance import calculate_junior_fee; print(calculate_junior_fee(1, '2026-01'))"
+//	PYTHONPATH=legacy/scripts:legacy python3 -c "from attendance import calculate_junior_fee; print(calculate_junior_fee(1, '2026-01'))"
 
 func TestCalculateJuniorFeeParity(t *testing.T) {
 	t.Parallel()

go/tests/parity/pure/format_date/format_date_parity_test.go

@@ -12,7 +12,7 @@ import (
 
 // Verify expected values against live Python:
 //
-//	PYTHONPATH=scripts:. python3 -c "from match_payments import format_date; print(format_date(46027))"
+//	PYTHONPATH=legacy/scripts:legacy python3 -c "from match_payments import format_date; print(format_date(46027))"
 
 func TestFormatDateParity(t *testing.T) {
 	t.Parallel()

go/tests/parity/pure/generate_sync_id/generate_sync_id_parity_test.go

@@ -12,7 +12,7 @@ import (
 
 // Verify expected values against live Python:
 //
-//	PYTHONPATH=scripts:. python3 -c "
+//	PYTHONPATH=legacy/scripts:legacy python3 -c "
 //	from sync_fio_to_sheets import generate_sync_id
 //	print(generate_sync_id({'date':'2026-01-15','amount':750.0,'currency':'CZK','sender':'Test','vs':'123','message':'x','bank_id':'1'}))"
 //

go/tests/parity/pure/infer_transaction_details/infer_transaction_details_parity_test.go

@@ -12,7 +12,7 @@ import (
 
 // Verify expected values against live Python:
 //
-//	PYTHONPATH=scripts:. python3 -c "
+//	PYTHONPATH=legacy/scripts:legacy python3 -c "
 //	from match_payments import infer_transaction_details
 //	print(infer_transaction_details({'sender':'Henrietta Ottová','message':'leden 2026','user_id':'','date':'2026-01-15'}, ['Henrietta Ottová']))"
 

go/tests/parity/pure/match_members/match_members_parity_test.go

@@ -12,7 +12,7 @@ import (
 
 // Verify expected values against live Python:
 //
-//	PYTHONPATH=scripts:. python3 -c "from match_payments import match_members; print(match_members('henrietta ottova leden', ['Henrietta Ottová','Jan Novák']))"
+//	PYTHONPATH=legacy/scripts:legacy python3 -c "from match_payments import match_members; print(match_members('henrietta ottova leden', ['Henrietta Ottová','Jan Novák']))"
 
 func TestMatchMembersParity(t *testing.T) {
 	t.Parallel()

go/tests/parity/pure/normalize/normalize_parity_test.go

@@ -12,7 +12,7 @@ import (
 
 // Verify expected values against live Python:
 //
-//	PYTHONPATH=scripts:. python3 -c "from czech_utils import normalize; print(normalize('štefan čakrtový'))"
+//	PYTHONPATH=legacy/scripts:legacy python3 -c "from czech_utils import normalize; print(normalize('štefan čakrtový'))"
 
 func TestNormalizeParity(t *testing.T) {
 	t.Parallel()

go/tests/parity/pure/parse_czk_amount/parse_czk_amount_parity_test.go

@@ -12,7 +12,7 @@ import (
 
 // Verify expected values against live Python:
 //
-//	PYTHONPATH=scripts:. python3 -c "from infer_payments import parse_czk_amount; print(parse_czk_amount('1.500,00'))"
+//	PYTHONPATH=legacy/scripts:legacy python3 -c "from infer_payments import parse_czk_amount; print(parse_czk_amount('1.500,00'))"
 //
 // Note: Go's ParseCZK returns an error for unparseable input; Python returns 0.0.
 // Callers should discard the error to match Python semantics: v, _ := money.ParseCZK(s)

go/tests/parity/pure/parse_month_references/parse_month_references_parity_test.go

@@ -13,7 +13,7 @@ import (
 
 // Verify expected values against live Python:
 //
-//	PYTHONPATH=scripts:. python3 -c "from czech_utils import parse_month_references; print(parse_month_references('prosinec-leden', 2026))"
+//	PYTHONPATH=legacy/scripts:legacy python3 -c "from czech_utils import parse_month_references; print(parse_month_references('prosinec-leden', 2026))"
 
 func TestParseMonthReferencesParity(t *testing.T) {
 	t.Parallel()

go/tests/parity/reconcile/reconcile_parity_test.go

@@ -6,7 +6,7 @@
 //
 // Verify expected values against live Python:
 //
-//	PYTHONPATH=scripts:. python3 -c "
+//	PYTHONPATH=legacy/scripts:legacy python3 -c "
 //	from match_payments import reconcile
 //	# ... build members/months/txs/exceptions...
 //	import json; print(json.dumps(reconcile(...)))"