feat(go): fixture capture + characterization framework (M3)

Closes M3.1–M3.6.  Parity safety net proving Go output matches Python
for every ported pure-domain function (M2.1–M2.9) and reconcile (M2.10).

Capture pipeline:
- scripts/capture_fixtures.py: calls each Python function with seeded
  inputs, emits JSON fixtures to stdout (never writes files directly).
- scripts/scrub_fixtures.py: deterministic PII scrubber — SHA-256
  pseudonyms for member names, digit-preserving hashes for VS/account/
  bank_id, name-sweep in message text.  Idempotent; no salt.
- scripts/_fixture_seeds.py: handcrafted seeds for all 11 functions;
  synthetic names throughout (no real roster members).
- scripts/capture_all_fixtures.sh: convenience wrapper for full corpus
  regeneration outside of make.

Fixture corpus (98 files, all PII-free):
- go/tests/fixtures/pure/<func>/<case>.json — 10 function directories.
- go/tests/fixtures/reconcile/<NN>_<case>.json — 10 branch-coverage
  cases: greedy, overpayment credit, proportional remainder, even-split,
  out-of-window, exception override, other: purpose, junior ?, multi-
  person+month fan-out, unmatched.

Go parity tests (//go:build parity):
- go/tests/parity/parityio.go: generic LoadDir/RunAll helpers + typed
  In/Out struct pairs for all 10 pure functions; Envelope decoder for
  int/float/none disambiguation.
- 10 pure-function test packages + bespoke reconcile test with per-cell
  float tolerance (math.Abs <= 0.01 for `paid` values).

Makefile: go-parity, go-test-all, capture-fixtures targets.
go/tests/fixtures/README.md: refresh workflow + PII audit guide.

Gate: make go-test green, make go-parity green (11/11 packages),
      make go-lint clean (parity tag), make go-build clean.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

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

@@ -0,0 +1,48 @@
+//go:build parity
+
+package infer_transaction_details_parity_test
+
+import (
+	"fuj-management/go/internal/domain/matching"
+	"fuj-management/go/tests/parity"
+	"reflect"
+	"testing"
+)
+
+// Verify expected values against live Python:
+//
+//	PYTHONPATH=scripts:. 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']))"
+
+func TestInferTransactionDetailsParity(t *testing.T) {
+	t.Parallel()
+	parity.RunAll(t, "../../../fixtures/pure/infer_transaction_details",
+		func(in parity.InferTxDetailsIn) parity.InferTxDetailsOut {
+			tx := matching.Transaction{
+				Sender:  in.Tx.Sender,
+				Message: in.Tx.Message,
+				UserID:  in.Tx.UserID,
+				Date:    in.Tx.Date.AsAny(),
+			}
+			result := matching.InferTransactionDetails(tx, in.MemberNames, in.DefaultYear)
+
+			matches := make([]parity.MatchResult, len(result.Members))
+			for i, m := range result.Members {
+				matches[i] = parity.MatchResult{Name: m.Name, Confidence: string(m.Confidence)}
+			}
+			months := result.Months
+			if months == nil {
+				months = []string{}
+			}
+			return parity.InferTxDetailsOut{
+				Matches:    matches,
+				Months:     months,
+				SearchText: result.SearchText,
+			}
+		},
+		func(want, got parity.InferTxDetailsOut) bool {
+			return reflect.DeepEqual(want, got)
+		},
+	)
+}