Add Import/Export for profile lists

File -> Export Profiles... writes all profiles (plus explicit, including
empty, folders) to a JSON file. File -> Import Profiles... reads one back,
recreates folders, and inserts profiles as new rows so IDs never collide
with the destination database. No credentials are ever persisted on a
Profile in the first place (only privateKeyPath, a filesystem path), so
nothing sensitive is exposed by an exported file.

Verified with a standalone headless round-trip test against isolated
app-data databases (SSH + RDP profiles, nested folders, all fields);
caught and fixed a bug where import was redundantly creating an explicit
folder row per profile that didn't exist in the original export.

Fixes #17.

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

src/session_window.cpp

@@ -170,6 +170,9 @@ SessionWindow::SessionWindow(QWidget* parent)
     QAction* newProfileAction = fileMenu->addAction(QStringLiteral("New Profile"));
     QAction* newFolderAction = fileMenu->addAction(QStringLiteral("New Folder"));
     fileMenu->addSeparator();
+    QAction* importProfilesAction = fileMenu->addAction(QStringLiteral("Import Profiles..."));
+    QAction* exportProfilesAction = fileMenu->addAction(QStringLiteral("Export Profiles..."));
+    fileMenu->addSeparator();
     QAction* quitAction = fileMenu->addAction(QStringLiteral("Quit"));
 
     connect(newProfileAction,
@@ -180,6 +183,14 @@ SessionWindow::SessionWindow(QWidget* parent)
             &QAction::triggered,
             this,
             [this]() { m_profilesWidget->createFolderInCurrentContext(); });
+    connect(importProfilesAction,
+            &QAction::triggered,
+            this,
+            [this]() { m_profilesWidget->importProfiles(); });
+    connect(exportProfilesAction,
+            &QAction::triggered,
+            this,
+            [this]() { m_profilesWidget->exportProfiles(); });
     connect(quitAction, &QAction::triggered, this, []() { qApp->quit(); });
 
     QMenu* helpMenu = menuBar()->addMenu(QStringLiteral("Help"));