viewer: add a Browse button to the processing output prefix

The output prefix was a plain text field; add a 'Browse…' button that opens a
file dialog to pick the output location. The chosen name is treated as a prefix
(the _process.h5 / .mtz / .cif suffixes are appended), so a trailing extension is
dropped, and the result is stored with native separators.

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

viewer/windows/JFJochProcessingJobsWindow.cpp

@@ -13,6 +13,7 @@
 #include <QDateTime>
 #include <QDialog>
 #include <QDir>
+#include <QFileDialog>
 #include <QFont>
 #include <QIcon>
 #include <QDialogButtonBox>
@@ -157,6 +158,24 @@ int JFJochProcessingJobsWindow::askJob(const ReprocessingInputs &inputs, JobSpec
         QStringLiteral("%1/%2_run%3").arg(fi.absolutePath(), stem).arg(job_counter_ + 1));
     auto *prefix = new QLineEdit(default_prefix, &dlg);
 
+    // "Browse…" opens a file dialog to choose where the outputs go. The chosen name is used as a prefix
+    // (suffixes like _process.h5 / .cif are appended), so drop a trailing extension.
+    auto *browse = new QPushButton("Browse…", &dlg);
+    connect(browse, &QPushButton::clicked, &dlg, [&dlg, prefix] {
+        const QString sel = QFileDialog::getSaveFileName(&dlg, "Output file prefix", prefix->text(),
+                                                         "All Files (*)", nullptr,
+                                                         QFileDialog::DontConfirmOverwrite);
+        if (sel.isEmpty())
+            return;
+        const QFileInfo pf(sel);
+        prefix->setText(QDir::toNativeSeparators(pf.dir().filePath(pf.completeBaseName())));
+    });
+    auto *prefixRow = new QWidget(&dlg);
+    auto *prefixRowLayout = new QHBoxLayout(prefixRow);
+    prefixRowLayout->setContentsMargins(0, 0, 0, 0);
+    prefixRowLayout->addWidget(prefix);
+    prefixRowLayout->addWidget(browse);
+
     // 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.
     auto *scaling = new QCheckBox("Scale && merge", &dlg);
@@ -169,7 +188,7 @@ int JFJochProcessingJobsWindow::askJob(const ReprocessingInputs &inputs, JobSpec
     form->addRow("Threads", threads);
     form->addRow(save_h5);
     form->addRow(save_merged);
-    form->addRow("Output prefix", prefix);
+    form->addRow("Output prefix", prefixRow);
     form->addRow(scaling);
 
     int result = 0;