viewer: write processing output next to the input file

The New-job dialog seeded the output prefix from QFileInfo::completeBaseName(),
which drops the directory, so _process.h5/.cif/.mtz landed in the viewer's
working directory (wherever it was installed) instead of beside the dataset.
Seed it with the input file's absolute directory instead; the field stays
editable. Relies on the trusted output-path support so the absolute prefix is
accepted by the writer.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

viewer/windows/JFJochProcessingJobsWindow.cpp

@@ -12,6 +12,7 @@
 #include <QComboBox>
 #include <QDateTime>
 #include <QDialog>
+#include <QDir>
 #include <QFont>
 #include <QIcon>
 #include <QDialogButtonBox>
@@ -140,8 +141,14 @@ int JFJochProcessingJobsWindow::askJob(const ReprocessingInputs &inputs, JobSpec
     auto *save = new QCheckBox("Save _process.h5", &dlg);
     save->setChecked(true);
 
-    const QString stem = QFileInfo(inputs.file).completeBaseName().remove(QStringLiteral("_master"));
-    auto *prefix = new QLineEdit(QStringLiteral("%1_run%2").arg(stem).arg(job_counter_ + 1), &dlg);
+    // Default the output next to the input file, not the viewer's working directory (the viewer starts
+    // wherever it was installed). This is an absolute path; Rugnux writes it via the trusted setter,
+    // and toNativeSeparators keeps a UNC/Windows path openable afterwards.
+    const QFileInfo fi(inputs.file);
+    const QString stem = fi.completeBaseName().remove(QStringLiteral("_master"));
+    const QString default_prefix = QDir::toNativeSeparators(
+        QStringLiteral("%1/%2_run%3").arg(fi.absolutePath(), stem).arg(job_counter_ + 1));
+    auto *prefix = new QLineEdit(default_prefix, &dlg);
 
     // Rotation-vs-stills mode (rotation indexing + partiality + rot3d) is set in the settings panel via
     // "Process as stills"; the dialog only collects run options. Scaling applies to MX full analysis.