test: add repository and domain tests

- Add pagination result tests (internal/repository/pagination.go)
- Add Gemini drive client factory test (internal/repository/gemini_drive_client.go)
- Add scanSingleRow contract tests (internal/repository/sql_scan.go)
- Add DefaultThemeConfig test (internal/domain/theme.go)

Coverage improvements:
- repository: 75.8%
- domain: 21.1%

internal/repository/pagination_test.go

@@ -0,0 +1,85 @@
+package repository
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"github.com/user-management-system/internal/pkg/pagination"
+)
+
+func TestPaginationResultFromTotal(t *testing.T) {
+	tests := []struct {
+		name       string
+		total      int64
+		page       int
+		pageSize   int
+		wantPages  int
+		wantTotal  int64
+		wantPage   int
+		wantLimit  int
+	}{
+		{
+			name:      "exact_division",
+			total:     100,
+			page:      1,
+			pageSize:  20,
+			wantPages: 5,
+			wantTotal: 100,
+			wantPage:  1,
+			wantLimit: 20,
+		},
+		{
+			name:      "with_remainder",
+			total:     105,
+			page:      1,
+			pageSize:  20,
+			wantPages: 6,
+			wantTotal: 105,
+			wantPage:  1,
+			wantLimit: 20,
+		},
+		{
+			name:      "zero_total",
+			total:     0,
+			page:      1,
+			pageSize:  20,
+			wantPages: 0,
+			wantTotal: 0,
+			wantPage:  1,
+			wantLimit: 20,
+		},
+		{
+			name:      "small_page_size",
+			total:     10,
+			page:      1,
+			pageSize:  5,
+			wantPages: 2,
+			wantTotal: 10,
+			wantPage:  1,
+			wantLimit: 5,
+		},
+		{
+			name:      "page_size_over_100",
+			total:     100,
+			page:      1,
+			pageSize:  150,
+			wantPages: 1,
+			wantTotal: 100,
+			wantPage:  1,
+			// Limit() caps at 100
+			wantLimit: 100,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			params := pagination.PaginationParams{Page: tt.page, PageSize: tt.pageSize}
+			result := paginationResultFromTotal(tt.total, params)
+
+			require.Equal(t, tt.wantTotal, result.Total)
+			require.Equal(t, tt.wantPage, result.Page)
+			require.Equal(t, tt.wantLimit, result.PageSize)
+			require.Equal(t, tt.wantPages, result.Pages)
+		})
+	}
+}