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/qetgraphicsitem/element.cpp

@@ -1345,7 +1345,8 @@ bool Element::removeTextFromGroup(DynamicElementTextItem *text,
 	The first Terminal of QPair is a Terminal owned by this element,
 	this terminal haven't got any conductor docked.
 	The second Terminal of QPair is a Terminal owned by an other element,
-	which is aligned with the first Terminal. The second Terminal can have or not docked conductors.
+	which is aligned with the first Terminal. The second Terminal can have or not docked conductors,
+	but no more than the project's wires-per-terminal limit allows (discussion #1158).
 */
 QList <QPair <Terminal *, Terminal *> > Element::AlignedFreeTerminals() const
 {
@@ -1357,7 +1358,9 @@ QList <QPair <Terminal *, Terminal *> > Element::AlignedFreeTerminals() const
 		{
 			Terminal *other_terminal =
 					terminal -> alignedWithTerminal();
-			if (other_terminal)
+			if (other_terminal
+				&& terminal->hasRoomForWire()
+				&& other_terminal->hasRoomForWire())
 				list << qMakePair(terminal, other_terminal);
 		}
 	}