Give shapes, independent texts and images a persisted uuid

Elements, conductors, terminals and tables already carry a uuid. The
drawing furniture beside them did not, so a script or the MCP server could
only name a line, a box or a note by its index in a position-sorted list,
which shifts whenever one is added or removed.

- QetShapeItem, IndependentTextItem and DiagramImageItem get uuid(),
  newUuid() and setUuid(), read from and written to a "uuid" attribute.
- A folio loaded from a file written before this (or carrying a duplicate
  uuid) derives one from the folio uuid, the item kind and its order in the
  file, so the same file gives the same uuids on every load and a re-save
  is stable -- the #754 lesson for conductors.
- Paste and folio duplication renew them, as they already do for elements
  and conductors.
- Scripting: texts(), shapes() and images() end each line with the uuid;
  textIndex(), shapeIndex() and imageIndex() turn one back into an index.
- misc/qet-mcp: qet_diff keys texts, shapes and images on uuid when both
  sides have one, so a move or edit reads as a change to that item.

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

sources/scripting/qetscriptapi.h

@@ -139,14 +139,13 @@ class QetGraphicsTableItem;
 	  style editor changes.
 
 	  These are addressed by @b index into a listing sorted by position
-	  (top to bottom, then left to right), because unlike an element they
-	  carry no uuid and unlike a conductor they have no terminal to be
-	  named by. Position is the only identity they have, and it persists,
-	  so the ordering is the same after a save and reload -- verified
-	  against exactly that. What it is @b not stable against is adding or
-	  deleting one: indexes after the affected position shift, the way a
-	  list's do. Call texts() or shapes() again rather than holding an
-	  index across an edit that adds or removes one.
+	  (top to bottom, then left to right), and the ordering is the same
+	  after a save and reload -- verified against exactly that. What it is
+	  @b not stable against is adding or deleting one: indexes after the
+	  affected position shift, the way a list's do. Each listing line ends
+	  with the item's uuid, which is persisted and does not shift: hold
+	  that across an edit, and turn it back into an index with textIndex(),
+	  shapeIndex() or imageIndex() when calling.
 	- @b Querying the project database: run a read-only SELECT against the
 	  SQLite database QElectroTech builds from the project, and get rows
 	  back as objects. This is not a new door. QET already ships a
@@ -432,6 +431,7 @@ class QetScriptApi : public QObject
 
 		// -- independent text and drawing shapes --
 		Q_INVOKABLE QStringList texts(int folioIndex) const;
+		Q_INVOKABLE int textIndex(int folioIndex, const QString &uuid) const;
 		Q_INVOKABLE int addText(int folioIndex, const QString &text, double x, double y);
 		Q_INVOKABLE QString textContent(int folioIndex, int textIndex) const;
 		Q_INVOKABLE bool setTextContent(int folioIndex, int textIndex, const QString &text);
@@ -440,6 +440,7 @@ class QetScriptApi : public QObject
 		Q_INVOKABLE bool deleteText(int folioIndex, int textIndex);
 
 		Q_INVOKABLE QStringList shapes(int folioIndex) const;
+		Q_INVOKABLE int shapeIndex(int folioIndex, const QString &uuid) const;
 		Q_INVOKABLE int addShape(int folioIndex, const QString &type,
 								 double x1, double y1, double x2, double y2);
 		Q_INVOKABLE bool deleteShape(int folioIndex, int shapeIndex);
@@ -496,6 +497,7 @@ class QetScriptApi : public QObject
 
 		// -- images, embedded in the project --
 		Q_INVOKABLE QStringList images(int folioIndex) const;
+		Q_INVOKABLE int imageIndex(int folioIndex, const QString &uuid) const;
 		Q_INVOKABLE int addImage(int folioIndex, const QString &filePath, double x, double y);
 		Q_INVOKABLE bool setImageScale(int folioIndex, int imageIndex, double factor);
 		Q_INVOKABLE bool setImageRotation(int folioIndex, int imageIndex, double angle);