Edit increment and preview the next number in the auto-numbering dock

Bug #331: "Il serait intéressant de pouvoir directement dans la fenêtre
'Sélection numérotation auto' modifier la valeur d'incrément et visualiser
la prochaine numérotation qui sera appliquée. Ceci sans être obligé
d'ouvrir la page de configuration."

The dock (AutoNumberingDockWidget) already let you see and edit a rule's
*current* value inline (added in 52c8ef6b4/031710b5f/ee4ba82d2). The
increment itself, and any preview of where the numbering is headed, was
reachable only through Configurer -> the full project-properties dialog.

Two new widgets per row (conductor/element/folio):

- An increment spin box, read from and written to the same NumerotationContext
  field NumPartEditorW's increase_spinBox already edits in the full dialog --
  same data, second place to reach it.
- A read-only next-value field, computed via
  NumerotationContextCommands::next() -- the identical engine the "Suivant"
  button in the full dialog already uses to step a whole context. Reusing it
  rather than reimplementing the arithmetic means wrap-and-carry between parts
  comes out identical to what actually happens when the number is next
  consumed, and zero-padding matches real rendering
  (NumerotationContext::formatValue(), mirroring
  autonum::setSequentialToList()'s padding rule by hand since that function is
  local to assignvariables.cpp).

NumerotationContext gains replaceIncrease(index, increase), a sibling to the
existing replaceValue() that touches only the increment field.

Every refresh call site in the file (13 of them) previously refreshed just the
value field; they now go through a new refreshRow(category), which refreshes
value + increment + next-value-preview together via a small per-row widget
bundle (rowFor()). This also let resetAutoNum()'s three-way switch collapse to
one line, and refreshValueFields()'s three near-identical blocks collapse to a
loop -- both existing before this change, not new here.

Verified live under Xvfb: created an element numbering rule "K" (Chiffre 1,
value 1, increment 1) via the full dialog, confirmed the dock showed
Valeur=1/Incrément=1/Suivant=2. Changed the dock's own Incrément to 3 --
Suivant updated live to 4, no dialog needed. Changed Valeur to 10 -- Suivant
became 13. Reopened the full configuration dialog and confirmed it read back
the same value_field=10/increase_spinBox=3, i.e. the round trip through
replaceIncrease()/storeContext() does not disturb type, initial value, modulus
or format.

Builds clean, CMake/Ninja Release, Qt 5.15, 820/820, no new warnings.

Fixes: https://qelectrotech.org/bugtracker/view.php?id=331

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

sources/autoNum/ui/autonumberingdockwidget.h

@@ -25,6 +25,7 @@
 
 class QComboBox;
 class QLineEdit;
+class QSpinBox;
 
 namespace Ui {
 	class AutoNumberingDockWidget;
@@ -66,12 +67,28 @@ class AutoNumberingDockWidget : public QDockWidget
 		void on_m_element_value_le_editingFinished();
 		void on_m_folio_value_le_editingFinished();
 
+		void on_m_conductor_increase_sb_valueChanged(int);
+		void on_m_element_increase_sb_valueChanged(int);
+		void on_m_folio_increase_sb_valueChanged(int);
+
 	signals:
 		void folioAutoNumChanged(QString);
 
 	private:
 		enum class AutoNumCategory { Conductor, Element, Folio };
 
+			/// The four widgets that make up one category's row, bundled so
+			/// refreshRow() can be called with just a category instead of
+			/// four pointers that must always be passed in matching sets.
+		struct Row
+		{
+			QComboBox *combo;
+			QLineEdit *value;
+			QSpinBox  *increase;
+			QLineEdit *next;
+		};
+		Row rowFor(AutoNumCategory category) const;
+
 		/**
 			@brief resetAutoNum
 			Reset the numerotation context currently selected in combo_box
@@ -93,6 +110,23 @@ class AutoNumberingDockWidget : public QDockWidget
 		void refreshValueField(QComboBox *combo_box, QLineEdit *line_edit, AutoNumCategory category);
 		void applyValueField(QComboBox *combo_box, QLineEdit *line_edit, AutoNumCategory category);
 
+			/// Refresh/apply the increment spin box the same way.
+		void refreshIncreaseField(QComboBox *combo_box, QSpinBox *increase_sb, AutoNumCategory category);
+		void applyIncreaseField(QComboBox *combo_box, QSpinBox *increase_sb, AutoNumCategory category);
+
+			/// Show what the counter will read after one more step, using
+			/// the same NumerotationContextCommands engine the Suivant
+			/// button in the full configuration dialog already advances
+			/// the whole context with -- so the preview can never disagree
+			/// with what actually happens when the number is next consumed.
+		void refreshNextField(QComboBox *combo_box, QLineEdit *next_edit, AutoNumCategory category);
+
+			/// Refresh a whole row -- value, increment and next-value
+			/// preview -- in one call. Every refresh call site needs the
+			/// increment and preview kept in step with the value now, so
+			/// this replaces refreshValueField() at each of them.
+		void refreshRow(AutoNumCategory category);
+
 		Ui::AutoNumberingDockWidget *ui;
 		QETProject* m_project = nullptr;
 		ProjectView* m_project_view = nullptr;