fix: check errors in test helpers and simplify nil-reader tests

Address Copilot review comments on PR mendixlabs#255:
- Check INSERT OR IGNORE error in setupMicroflowsDB (empty_test.go)
- Check INSERT OR IGNORE error in setupEntitiesDB (domain_size_test.go)
- Pass nil db directly in SEC002/SEC003 nil-reader tests (security_test.go)
- Remove unused sql/sqlite imports from security_test.go

Author: retran

mdl/linter/rules/domain_size_test.go

@@ -42,7 +42,9 @@ func setupEntitiesDB(t *testing.T, entities [][]any) *sql.DB {
 			t.Fatalf("failed to insert entity: %v", err)
 		}
 		moduleName := row[3].(string)
-		db.Exec(`INSERT OR IGNORE INTO modules (Name, Source) VALUES (?, '')`, moduleName)
+		if _, err := db.Exec(`INSERT OR IGNORE INTO modules (Name, Source) VALUES (?, '')`, moduleName); err != nil {
+			t.Fatalf("failed to insert module: %v", err)
+		}
 	}
 
 	return db

mdl/linter/rules/empty_test.go

@@ -42,7 +42,9 @@ func setupMicroflowsDB(t *testing.T, rows [][]any) *sql.DB {
 		}
 		// Ensure module exists
 		moduleName := row[3].(string)
-		db.Exec(`INSERT OR IGNORE INTO modules (Name, Source) VALUES (?, '')`, moduleName)
+		if _, err := db.Exec(`INSERT OR IGNORE INTO modules (Name, Source) VALUES (?, '')`, moduleName); err != nil {
+			t.Fatalf("failed to insert module: %v", err)
+		}
 	}
 
 	return db

mdl/linter/rules/security_test.go

@@ -3,12 +3,9 @@
 package rules
 
 import (
-	"database/sql"
 	"testing"
 
 	"github.com/mendixlabs/mxcli/mdl/linter"
-
-	_ "modernc.org/sqlite"
 )
 
 func TestNoEntityAccessRulesRule_NoViolation(t *testing.T) {
@@ -93,10 +90,7 @@ func TestNoEntityAccessRulesRule_Metadata(t *testing.T) {
 // Full behavioral coverage requires integration tests with a real .mpr project.
 
 func TestWeakPasswordPolicyRule_NilReader(t *testing.T) {
-	db, _ := sql.Open("sqlite", ":memory:")
-	defer db.Close()
-
-	ctx := linter.NewLintContextFromDB(db)
+	ctx := linter.NewLintContextFromDB(nil)
 	rule := NewWeakPasswordPolicyRule()
 	violations := rule.Check(ctx)
 
@@ -116,10 +110,7 @@ func TestWeakPasswordPolicyRule_Metadata(t *testing.T) {
 }
 
 func TestDemoUsersActiveRule_NilReader(t *testing.T) {
-	db, _ := sql.Open("sqlite", ":memory:")
-	defer db.Close()
-
-	ctx := linter.NewLintContextFromDB(db)
+	ctx := linter.NewLintContextFromDB(nil)
 	rule := NewDemoUsersActiveRule()
 	violations := rule.Check(ctx)