Merge Profiles and Session windows into a single window

ProfilesWindow and SessionWindow were two independent top-level windows,
coordinated through a QPointer and manual show/create-or-reuse logic, with
duplicated Help menus and a path where Quit didn't actually quit if a
SessionWindow happened to be open. ProfilesWindow is now an embedded QWidget
shown as a permanent, unclosable "Profiles" tab inside SessionWindow's tab
widget; SessionWindow is the app's sole top-level window. Double-clicking a
profile opens a session tab in the same window instead of finding-or-creating
a second one, and closing all session tabs falls back to the Profiles tab
rather than closing the app.

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

src/profiles_window.h

@@ -3,7 +3,7 @@
 
 #include "profile_repository.h"
 
-#include <QMainWindow>
+#include <QWidget>
 #include <QString>
 #include <QStringList>
 #include <QtGlobal>
@@ -11,7 +11,6 @@
 #include <memory>
 #include <map>
 #include <optional>
-#include <QPointer>
 #include <vector>
 #include <unordered_map>
 
@@ -21,10 +20,9 @@ class QLineEdit;
 class QPushButton;
 class QComboBox;
 class QPoint;
-class SessionWindow;
 class ProfilesTreeWidget;
 
-class ProfilesWindow : public QMainWindow
+class ProfilesWindow : public QWidget
 {
     Q_OBJECT
 
@@ -32,6 +30,12 @@ public:
     explicit ProfilesWindow(QWidget* parent = nullptr);
     ~ProfilesWindow() override;
 
+    void createProfileInCurrentContext();
+    void createFolderInCurrentContext();
+
+signals:
+    void connectRequested(const Profile& profile);
+
 private:
     QLineEdit* m_searchBox;
     QComboBox* m_viewModeBox;
@@ -42,7 +46,6 @@ private:
     QPushButton* m_newButton;
     QPushButton* m_editButton;
     QPushButton* m_deleteButton;
-    QPointer<SessionWindow> m_sessionWindow;
     std::unique_ptr<ProfileRepository> m_repository;
     std::unordered_map<qint64, Profile> m_profileCache;
     QString m_pendingTagFilterPreference;