Add a wires-per-terminal limit, with an application master switch

Discussion #1158: a real terminal takes one or two wires (four with
double ferrules), a folio report is a virtual point that carries one, but
QElectroTech lets any number of wires be connected anywhere.

Project properties > General gets a "Conducteurs par borne" group:
- the most wires a terminal may take (0, the default, is no limit);
- "one wire per folio report".
When set, a new wire that would go past the limit is refused: the
terminal shows red while dragging, as for any refused link, and a tooltip
says why on release. Auto-connect on placing, moving or multi-pasting a
symbol skips full terminals, and qet.addConductor() refuses with its own
message. Wires already drawn, opening, pasting and undo are never
refused.

Settings > General gets a master switch, on by default, that turns every
rule of this feature off in every project; the project group is greyed
with a note while it is off.

The rules live in wiringrules.cpp. The project setting is saved as
<wiring_rules .../> only when a rule is on, so a project that never used
it saves exactly as before; an older version drops it, which means "off".

tst_wiringrules covers the rules, the save round trip and, through the
real binary, that a wire past the limit is refused unless the master
switch is off (checked to fail with the limit check removed).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015FPuYPS4T7QuEwjNu22rXD

sources/qetproject.cpp

@@ -1257,6 +1257,26 @@ void QETProject::setWireHops(WireHops::Mode mode)
 	}
 }
 
+/**
+	@brief QETProject::wiringRules
+	@return how many wires a terminal of this project may take
+	(discussion #1158); the default when the project sets no rule.
+*/
+WiringRules::Settings QETProject::wiringRules() const {
+	return m_wiring_rules;
+}
+
+/**
+	@brief QETProject::setWiringRules
+	Set how many wires a terminal of this project may take. Only wires
+	drawn from now on are affected: none already drawn is removed.
+	@param rules
+*/
+void QETProject::setWiringRules(const WiringRules::Settings &rules)
+{
+	m_wiring_rules = rules;
+}
+
 /**
 	@brief QETProject::autoBreakConductor
 	@return true if use of auto break conductor is authorized.
@@ -1367,6 +1387,7 @@ QDomDocument QETProject::toXml()
 	// local, non-transmitted usage tracking (time spent on this project)
 	writeUsageXml(project_root);
 	writeWireHopsXml(project_root);
+	writeWiringRulesXml(project_root);
 
 	// Properties for news diagrams
 	QDomElement new_diagrams_properties = xml_doc.createElement("newdiagrams");
@@ -1877,6 +1898,7 @@ void QETProject::readProjectXml(QDomDocument &xml_project)
 		//Load the local, non-transmitted usage tracking
 	readUsageXml(xml_project);
 	readWireHopsXml(xml_project);
+	readWiringRulesXml(xml_project);
 
 		//Load the default properties for the new diagrams
 	readDefaultPropertiesXml(xml_project);
@@ -2070,6 +2092,17 @@ void QETProject::readWireHopsXml(QDomDocument &xml_project)
 			: WireHops::fromString(crossings.attribute(QStringLiteral("hop")));
 }
 
+/**
+	@brief QETProject::readWiringRulesXml
+	Read the <wiring_rules> element of the project, if any.
+	A project without it sets no rule.
+	@param xml_project : the xml description of the project
+*/
+void QETProject::readWiringRulesXml(QDomDocument &xml_project)
+{
+	m_wiring_rules = WiringRules::fromXml(xml_project.documentElement());
+}
+
 /**
 	@brief QETProject::readDefaultPropertiesXml
 	load default properties for new diagram, found in the xml of this project
@@ -2232,6 +2265,16 @@ void QETProject::writeWireHopsXml(QDomElement &xml_element)
 	xml_element.appendChild(crossings);
 }
 
+/**
+	@brief QETProject::writeWiringRulesXml
+	Export the project's wiring rules as a <wiring_rules> child of
+	\a xml_element, only when one is set.
+*/
+void QETProject::writeWiringRulesXml(QDomElement &xml_element)
+{
+	WiringRules::toXml(m_wiring_rules, xml_element);
+}
+
 /**
 	@brief QETProject::writeDefaultPropertiesXml
 	Export all defaults properties used by a new diagram and his content