Fix all static analysis errors (golangci-lint)

- Fix errcheck: handle all error return values in production code
- Fix errcheck: handle all error return values in test files
- Fix staticcheck: replace deprecated WithCredentialsFile with WithAuthCredentialsFile
- Remove unused code: authHeaders, planToEatPlannerItem, planToEatResponse
- Use defer func() { _ = x.Close() }() pattern for ignored close errors

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

1 files changed, 4 insertions, 4 deletions

diff --git a/internal/auth/auth_test.go b/internal/auth/auth_test.go
index 505efe3..013a4aa 100644
--- a/internal/auth/auth_test.go
+++ b/internal/auth/auth_test.go
@@ -15,7 +15,7 @@ func TestAuthenticate(t *testing.T) {
 	if err != nil {
 		t.Fatalf("an error '%s' was not expected when opening a stub database connection", err)
 	}
-	defer db.Close()
+	defer func() { _ = db.Close() }()
 
 	service := NewService(db)
 
@@ -34,7 +34,7 @@ func TestAuthenticate(t *testing.T) {
 		t.Errorf("expected no error, got %v", err)
 	}
 	if user == nil {
-		t.Errorf("expected user, got nil")
+		t.Fatal("expected user, got nil")
 	}
 	if user.Username != "testuser" {
 		t.Errorf("expected username testuser, got %s", user.Username)
@@ -50,7 +50,7 @@ func TestAuthenticate_InvalidCredentials(t *testing.T) {
 	if err != nil {
 		t.Fatalf("an error '%s' was not expected when opening a stub database connection", err)
 	}
-	defer db.Close()
+	defer func() { _ = db.Close() }()
 
 	service := NewService(db)
 
@@ -73,7 +73,7 @@ func TestCreateUser(t *testing.T) {
 	if err != nil {
 		t.Fatalf("an error '%s' was not expected when opening a stub database connection", err)
 	}
-	defer db.Close()
+	defer func() { _ = db.Close() }()
 
 	service := NewService(db)