Live mode: an AI assistant acts on the open project while the user watches

A new setting, Configurer QElectroTech > Général > "Autoriser un assistant
IA à agir sur le projet ouvert", off by default. Off, nothing changes:
no channel is opened. On, every start shows a warning first -- Continuer,
Pas pour cette session, or Désactiver -- and nothing can connect until
the user answers Continuer. It waits for any other start-up question to
be answered, so the two never stack.

Accepted, LiveServer opens a local socket only the user's account can
use, with a random name and token written to live-session.json in the
data folder for the qet MCP server, and removed when the channel closes.
One JSON request per line: status (project, folio on screen, selection,
last undo step, stored scripts), run_script and run_stored. Requests are
queued out of the socket handler before they run (the lesson of PR #861).

Each run is one undo step named "Assistant : <name>". The status bar
shows the mode and the assistant's last action with a ✓ or ✗ and the
time, and an Arrêter button that closes the channel for the session.
Unticking the setting closes it at once.

QetScripting::runSource() runs script text and, for a live run, returns
what qet.log() wrote, the error with its line and the undo step instead
of showing boxes; qet.showMessage() is logged rather than opening a box
nobody asked for.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

sources/scripting/qetscripting.h

@@ -64,6 +64,28 @@ namespace QetScripting {
 	bool runOnProject(const QString &scriptPath, QETProject *project, DiagramView *view = nullptr,
 			  const QString &title = QString());
 
+	/**
+		@brief What a live run (an assistant acting on the open project,
+		see LiveServer) reports instead of showing: what the script
+		logged, the error if it threw, and the undo step it left, empty
+		if it changed nothing.
+	*/
+	struct LiveRun
+	{
+		QStringList log;
+		QString error;
+		QString undoText;
+	};
+
+	/**
+		@brief Run @p source as runOnProject() runs a file. @p fileName is
+		what errors name; @p title names the undo step. With @p live, no
+		box is shown: qet.log() and errors are collected there, and
+		qet.showMessage() is logged rather than shown.
+	*/
+	bool runSource(const QString &source, const QString &fileName, const QString &title,
+		       QETProject *project, DiagramView *view, LiveRun *live);
+
 }
 
 #endif // QET_SCRIPTING_H