fix: comprehensive bug fixes and architecture restructuring

Phase 1 — Bug fixes (7 bugs):
- Bug 1: Pulsar mode data loss — always persist to SQLite regardless of mode
- Bug 2: PulsarSend closing TCP client — use independent resetPulsarProducer()
- Bug 3: Greedy regex — use non-greedy (?s)ZCZC.*?NNNN
- Bug 4: Data after NNNN discarded — keep remaining buffer data
- Bug 5: strings.Index > 0 boundary — use strings.Contains
- Bug 6: Variable shadowing in PulsarSend — use = not :=
- Bug 7: Accept failure nil panic — add continue + retry logic

Phase 2 — Architecture restructuring:
- Split utils/ into config/, serial/, telegram/, storage/, transport/
- Define Sender, Repository, Reader interfaces
- Introduce app/ layer with context.Context lifecycle
- Replace spinlock with sync.Mutex
- Unified Config struct replaces 15+ global vars

Phase 3 — Testing & tooling:
- telegram/parser_test.go (7 test cases)
- storage/store_test.go (5 test cases)
- transport/transport_test.go (4 test cases)
- Taskfile: add test, test-race, test-cover tasks
- Go version: 1.15 -> 1.21

transport/transport_test.go

@@ -0,0 +1,63 @@
+package transport
+
+import (
+	"errors"
+	"sync/atomic"
+	"testing"
+)
+
+// mockSender implements Sender for testing.
+type mockSender struct {
+	sendCount int32
+	lastSent  string
+	failCount int32
+	maxFails  int32
+}
+
+func (m *mockSender) Send(telegram string) error {
+	atomic.AddInt32(&m.sendCount, 1)
+	m.lastSent = telegram
+	if atomic.LoadInt32(&m.failCount) < atomic.LoadInt32(&m.maxFails) {
+		atomic.AddInt32(&m.failCount, 1)
+		return errors.New("mock send error")
+	}
+	return nil
+}
+
+func (m *mockSender) Close() error { return nil }
+
+func TestMultiSender_SendToAll(t *testing.T) {
+	s1 := &mockSender{}
+	s2 := &mockSender{}
+	ms := NewMultiSender(s1, s2)
+
+	err := ms.Send("ZCZC TEST NNNN")
+	if err != nil {
+		t.Fatalf("MultiSender.Send() failed: %v", err)
+	}
+
+	if s1.sendCount != 1 {
+		t.Errorf("expected s1.sendCount=1, got %d", s1.sendCount)
+	}
+	if s2.sendCount != 1 {
+		t.Errorf("expected s2.sendCount=1, got %d", s2.sendCount)
+	}
+}
+
+func TestMultiSender_Empty(t *testing.T) {
+	ms := NewMultiSender()
+	err := ms.Send("ZCZC TEST NNNN")
+	if err != nil {
+		t.Fatalf("MultiSender.Send() with no senders failed: %v", err)
+	}
+}
+
+func TestPulsarSender_Interface(t *testing.T) {
+	var s Sender = &mockSender{}
+	_ = s
+}
+
+func TestTCPSender_Interface(t *testing.T) {
+	s := NewTCPSender("127.0.0.1:9999")
+	var _ Sender = s
+}