H-127: align Captain inbox repository fixture (#20)

Co-authored-by: Rogee <rogee@ipao.vip>

backend/internal/repository/captain_inbox_repo_test.go

@@ -128,17 +128,15 @@ func TestCaptainInboxRepo_FindByInboxID(t *testing.T) {
 	db := setupTestDB(t, &model.CaptainInbox{})
 	repo := NewCaptainInboxRepo(db)
 
-	// Create multiple assistants linked to the same inbox
+	// Create bindings for different inboxes. An inbox has at most one active assistant.
 	ci1 := newTestCaptainInbox(6, 60, 600)
-	ci2 := newTestCaptainInbox(7, 60, 600) // same inbox, different assistant
-	ci3 := newTestCaptainInbox(8, 61, 600) // different inbox
+	ci2 := newTestCaptainInbox(7, 61, 600)
 	require.NoError(t, repo.Create(context.Background(), ci1))
 	require.NoError(t, repo.Create(context.Background(), ci2))
-	require.NoError(t, repo.Create(context.Background(), ci3))
 
 	inboxes, err := repo.FindByInboxID(context.Background(), 60)
 	require.NoError(t, err)
-	assert.Len(t, inboxes, 2, "should return 2 entries for inbox 60")
+	assert.Len(t, inboxes, 1, "should return the entry for inbox 60")
 
 	// Verify all results belong to the correct inbox
 	for _, ci := range inboxes {
@@ -153,4 +151,4 @@ func TestCaptainInboxRepo_FindByInboxID_Empty(t *testing.T) {
 	inboxes, err := repo.FindByInboxID(context.Background(), 999)
 	require.NoError(t, err)
 	assert.Empty(t, inboxes, "should return empty list for non-existent inbox")
-}
+}