refactor(test/mainwindow): use QDir::filePath() for .gpg-id path construction (#1491)

* refactor(test/mainwindow): use QDir::filePath() for .gpg-id path construction

QDir(dir).filePath(name) handles separator normalisation intrinsically
and is more idiomatic Qt than manual string concatenation + cleanPath.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix: apply CodeRabbit auto-fixes

Fixed 1 file(s) based on 1 unresolved review comment.

Co-authored-by: CodeRabbit <noreply@coderabbit.ai>

* style: apply clang-format to tst_mainwindow.cpp

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>
Co-authored-by: CodeRabbit <noreply@coderabbit.ai>

Author: 4 people

tests/auto/mainwindow/tst_mainwindow.cpp

@@ -65,7 +65,8 @@ void tst_mainwindow::initTestCase() {
   QVERIFY2(m_storeDir.isValid(), "temp store dir must be created");
 
   // Minimal valid pass store: just a .gpg-id file
-  QFile gpgId(QDir::cleanPath(m_storeDir.path() + QStringLiteral("/.gpg-id")));
+  QFile gpgId(QDir::cleanPath(
+      QDir(m_storeDir.path()).filePath(QStringLiteral(".gpg-id"))));
   QVERIFY2(gpgId.open(QIODevice::WriteOnly), ".gpg-id must be writable");
   gpgId.write("0000000000000000\n");
   gpgId.close();