edz: make EdzArchive error strings translatable (+ DE/FR)

The six user-facing error strings in EdzArchive::extract() were hard-coded
QStringLiteral, so they could not be translated (reported by plc-user in
PR #513).

Wrap them in tr() via Q_DECLARE_TR_FUNCTIONS — EdzArchive is not a QObject,
so this gives it its own translation context without pulling in a moc
dependency. The *.part.xml glob stays a QStringLiteral: it is a filename
pattern, not user-facing text.

Adds German and French translations for all six. German wording for
"Cannot read %1" is plc-user's ("Kann %1 nicht lesen.").

Note for review: the rest of QET uses French source strings translated to
en/de in the .ts files, whereas these strings are English in the source
(as merged in PR #513). This commit keeps them English rather than
rewriting strings already reviewed; happy to flip them to French sources
for consistency if preferred.

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

sources/import/edz/edzarchive.h

@@ -18,6 +18,7 @@
 #ifndef EDZARCHIVE_H
 #define EDZARCHIVE_H
 
+#include <QCoreApplication>
 #include <QString>
 #include <QScopedPointer>
 
@@ -38,6 +39,8 @@ class QTemporaryDir;
 */
 class EdzArchive
 {
+	Q_DECLARE_TR_FUNCTIONS(EdzArchive)
+
 	public:
 		EdzArchive();
 		~EdzArchive();