Add comprehensive kanban board tests and fix test suite

- Add 13 tests for task kanban categorization and button types
- Fix i18n initialization in test setup (was causing nil pointer panics)
- Add TaskCompletionImage to test DB auto-migrate
- Update ListTasks tests to expect kanban board response instead of array

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

internal/services/task_service_test.go

@@ -151,7 +151,13 @@ func TestTaskService_ListTasks(t *testing.T) {
 
 	resp, err := service.ListTasks(user.ID)
 	require.NoError(t, err)
-	assert.Len(t, resp, 3)
+	// ListTasks returns a KanbanBoardResponse with columns
+	// Count total tasks across all columns
+	totalTasks := 0
+	for _, col := range resp.Columns {
+		totalTasks += col.Count
+	}
+	assert.Equal(t, 3, totalTasks)
 }
 
 func TestTaskService_UpdateTask(t *testing.T) {