.qetz format 3: one project database (stage D3a)

project.sqlite now holds both what QElectroTech keeps in its project
database (the index D2 wrote as index.sqlite) and the document's
engineering data, the latter's tables named doc_<name> beside the
former's -- element, element_info, link and conductor exist in both
(QetContainerDb's SQL names them as before; Database::sql() puts the
prefix on). The manifest says format 3, min-reader 3: a format 2 reader
would find no tables of its names. Format 2 files, with or without an
index.sqlite entry, are read as before: the prefix is found from the
file (doc_meta).

A .qetz with an index opens from project.sqlite. Measured: the 136-folio
f2099 1.8 s, 5.2 MB (the two table sets still overlap: D3b).

Checked: tst_qetcontainer with the format 3 names, 34/34; a format 2 file
of the last commit opens from its index.sqlite and saves the same; corpus
342: 340 .qetz carry the index in project.sqlite and open from it, saved
back = eager = master on all 342. ctest 96/96 with and without
QET_LAZY_FOLIOS=1.

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

sources/container/qetcontainer.cpp

@@ -172,7 +172,7 @@ bool QetContainer::readDocument(const QByteArray &content, QDomDocument *documen
 	set if @p project is not a project
 */
 QList<QetZip::Entry> QetContainer::split(const QDomDocument &project, const QString &writer,
-										 QString *error)
+										 QString *error, const QByteArray &index)
 {
 	QDomDocument document = project.cloneNode(true).toDocument();
 	QDomElement root = document.documentElement();
@@ -182,7 +182,7 @@ QList<QetZip::Entry> QetContainer::split(const QDomDocument &project, const QStr
 	}
 
 		//The engineering data out of the document, into project.sqlite
-	const QByteArray database = QetContainerDb::extract(root, error);
+	const QByteArray database = QetContainerDb::extract(root, error, index);
 	if (database.isEmpty())
 		return {};