Wire up CTest and add unit test coverage for ProfileRepository

Adds a Qt6::Test-based unit test target (tests/test_profile_repository.cpp,
21 cases), gated behind an ORBITHUB_BUILD_TESTS option that no-ops
gracefully if Qt6::Test isn't available, so it can't break app-only
builds. Covers profile CRUD, validation rules, search/sort, tag
normalization, and folder handling, each against an isolated temporary
SQLite file (new ProfileRepository(databasePathOverride) constructor
overload added for exactly this).

Caught and fixed a real bug along the way: normalizedTags()'s result was
bound directly without the nonNullTrimmed() null-guard every other field
already uses, so creating a profile with no tags at all hit the `tags
NOT NULL` constraint and silently failed -- including via the Import
Profiles feature for any export where a profile has no tags key.

Partial progress on #1 (RdpSessionBackend/SshSessionBackend state-machine
coverage still open -- much larger lift, needs a testability pass on
those backends first).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/profile_repository.cpp

@@ -9,7 +9,11 @@
 #include <QVariant>
 #include <QStringList>
 
+#include <atomic>
+
 namespace {
+std::atomic<int> g_testConnectionCounter{0};
+
 QString buildDatabasePath()
 {
     QString appDataPath = QStandardPaths::writableLocation(QStandardPaths::AppDataLocation);
@@ -176,7 +180,7 @@ void bindProfileFields(QSqlQuery& query, const Profile& profile)
                              : QStringLiteral("Negotiate"));
     query.addBindValue(isRdp ? normalizedRdpPerformanceProfile(profile.rdpPerformanceProfile)
                              : QStringLiteral("Balanced"));
-    query.addBindValue(normalizedTags(profile.tags));
+    query.addBindValue(nonNullTrimmed(normalizedTags(profile.tags)));
 }
 
 Profile profileFromQuery(const QSqlQuery& query)
@@ -259,6 +263,16 @@ ProfileRepository::ProfileRepository() : m_connectionName(QStringLiteral("orbith
     }
 }
 
+ProfileRepository::ProfileRepository(const QString& databasePathOverride)
+    : m_connectionName(QStringLiteral("orbithub_test_%1")
+                            .arg(g_testConnectionCounter.fetch_add(1))),
+      m_databasePathOverride(databasePathOverride)
+{
+    if (!initializeDatabase()) {
+        QSqlDatabase::removeDatabase(m_connectionName);
+    }
+}
+
 ProfileRepository::~ProfileRepository()
 {
     if (QSqlDatabase::contains(m_connectionName)) {
@@ -485,7 +499,8 @@ bool ProfileRepository::deleteProfile(qint64 id) const
 bool ProfileRepository::initializeDatabase()
 {
     QSqlDatabase database = QSqlDatabase::addDatabase(QStringLiteral("QSQLITE"), m_connectionName);
-    database.setDatabaseName(buildDatabasePath());
+    database.setDatabaseName(
+        m_databasePathOverride.isEmpty() ? buildDatabasePath() : m_databasePathOverride);
 
     if (!database.open()) {
         m_initError = database.lastError().text();

src/profile_repository.h

@@ -35,6 +35,9 @@ class ProfileRepository
 {
 public:
     ProfileRepository();
+    // databasePathOverride lets tests point the repository at an isolated,
+    // disposable SQLite file instead of the real app-data location.
+    explicit ProfileRepository(const QString& databasePathOverride);
     ~ProfileRepository();
 
     QString initError() const;
@@ -51,6 +54,7 @@ public:
 
 private:
     QString m_connectionName;
+    QString m_databasePathOverride;
     QString m_initError;
     mutable QString m_lastError;