Coverage priorities 1-5: test pure functions, extract interfaces, mock-based handler tests

- Priority 1: Test NewSendEmailTask + NewSendPushTask (5 tests)
- Priority 2: Test customHTTPErrorHandler — all 15+ branches (21 tests)
- Priority 3: Extract Enqueuer interface + payload builders in worker pkg (5 tests)
- Priority 4: Extract ClassifyFile/ComputeRelPath in migrate-encrypt (6 tests)
- Priority 5: Define Handler interfaces, refactor to accept them, mock-based tests (14 tests)
- Fix .gitignore: /worker instead of worker to stop ignoring internal/worker/

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/dto/requests/requests_test.go

@@ -0,0 +1,130 @@
+package requests
+
+import (
+	"encoding/json"
+	"testing"
+	"time"
+)
+
+func TestFlexibleDate_UnmarshalJSON_DateOnly(t *testing.T) {
+	var fd FlexibleDate
+	err := fd.UnmarshalJSON([]byte(`"2025-11-27"`))
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	want := time.Date(2025, 11, 27, 0, 0, 0, 0, time.UTC)
+	if !fd.Time.Equal(want) {
+		t.Errorf("got %v, want %v", fd.Time, want)
+	}
+}
+
+func TestFlexibleDate_UnmarshalJSON_RFC3339(t *testing.T) {
+	var fd FlexibleDate
+	err := fd.UnmarshalJSON([]byte(`"2025-11-27T15:30:00Z"`))
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	want := time.Date(2025, 11, 27, 15, 30, 0, 0, time.UTC)
+	if !fd.Time.Equal(want) {
+		t.Errorf("got %v, want %v", fd.Time, want)
+	}
+}
+
+func TestFlexibleDate_UnmarshalJSON_Null(t *testing.T) {
+	var fd FlexibleDate
+	err := fd.UnmarshalJSON([]byte(`null`))
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if !fd.Time.IsZero() {
+		t.Errorf("expected zero time, got %v", fd.Time)
+	}
+}
+
+func TestFlexibleDate_UnmarshalJSON_EmptyString(t *testing.T) {
+	var fd FlexibleDate
+	err := fd.UnmarshalJSON([]byte(`""`))
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if !fd.Time.IsZero() {
+		t.Errorf("expected zero time, got %v", fd.Time)
+	}
+}
+
+func TestFlexibleDate_UnmarshalJSON_Invalid(t *testing.T) {
+	var fd FlexibleDate
+	err := fd.UnmarshalJSON([]byte(`"not-a-date"`))
+	if err == nil {
+		t.Fatal("expected error for invalid date, got nil")
+	}
+}
+
+func TestFlexibleDate_MarshalJSON_Valid(t *testing.T) {
+	fd := FlexibleDate{Time: time.Date(2025, 11, 27, 15, 30, 0, 0, time.UTC)}
+	data, err := fd.MarshalJSON()
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	var s string
+	if err := json.Unmarshal(data, &s); err != nil {
+		t.Fatalf("result is not a JSON string: %v", err)
+	}
+	want := "2025-11-27T15:30:00Z"
+	if s != want {
+		t.Errorf("got %q, want %q", s, want)
+	}
+}
+
+func TestFlexibleDate_MarshalJSON_Zero(t *testing.T) {
+	fd := FlexibleDate{}
+	data, err := fd.MarshalJSON()
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if string(data) != "null" {
+		t.Errorf("got %s, want null", string(data))
+	}
+}
+
+func TestFlexibleDate_ToTimePtr_Valid(t *testing.T) {
+	fd := &FlexibleDate{Time: time.Date(2025, 11, 27, 0, 0, 0, 0, time.UTC)}
+	ptr := fd.ToTimePtr()
+	if ptr == nil {
+		t.Fatal("expected non-nil pointer")
+	}
+	if !ptr.Equal(fd.Time) {
+		t.Errorf("got %v, want %v", *ptr, fd.Time)
+	}
+}
+
+func TestFlexibleDate_ToTimePtr_Zero(t *testing.T) {
+	fd := &FlexibleDate{}
+	ptr := fd.ToTimePtr()
+	if ptr != nil {
+		t.Errorf("expected nil, got %v", *ptr)
+	}
+}
+
+func TestFlexibleDate_ToTimePtr_NilReceiver(t *testing.T) {
+	var fd *FlexibleDate
+	ptr := fd.ToTimePtr()
+	if ptr != nil {
+		t.Errorf("expected nil for nil receiver, got %v", *ptr)
+	}
+}
+
+func TestFlexibleDate_RoundTrip(t *testing.T) {
+	original := FlexibleDate{Time: time.Date(2025, 6, 15, 10, 0, 0, 0, time.UTC)}
+	data, err := original.MarshalJSON()
+	if err != nil {
+		t.Fatalf("marshal error: %v", err)
+	}
+	var restored FlexibleDate
+	if err := restored.UnmarshalJSON(data); err != nil {
+		t.Fatalf("unmarshal error: %v", err)
+	}
+	if !original.Time.Equal(restored.Time) {
+		t.Errorf("round-trip mismatch: original %v, restored %v", original.Time, restored.Time)
+	}
+}