Address review feedback

- Make the step card keyboard-selectable. The card root's onClick was
  mouse-only; role="button" on the root is not an option because it wraps
  the parameter inputs, so the step title becomes a real button with
  aria-pressed, matching the canvas node pattern.
- Give the workflow canvas its own empty-state string. It rendered the
  same emptyPipelineHint the step list shows, so the identical sentence
  appeared twice whenever a model had no steps.
- Report fan-in as "Merging pipelines are not supported yet" instead of
  reusing the branching message, which misled on a merge import.
- Cover the cycle branch that the existing test never reached: its
  two-node loop carries two edges and is rejected by the earlier
  edge-count check, so add a three-node fixture with a chain-sized edge
  count that still leaves an untraversed loop, plus a merge-message test.

Author: giswqs

apps/geolibre-desktop/src/components/processing/ModelBuilderDialog.tsx

@@ -811,7 +811,7 @@ function WorkflowCanvas({
     >
       {steps.length === 0 ? (
         <p className="py-6 text-center text-xs text-muted-foreground">
-          {t("processing.modelBuilder.emptyPipelineHint")}
+          {t("processing.modelBuilder.canvasEmpty")}
         </p>
       ) : (
         <div className="flex min-w-max items-center py-2">
@@ -909,9 +909,17 @@ function StepCard({
       onClick={onSelect}
     >
       <div className="mb-2 flex items-center justify-between gap-2">
-        <span className="truncate text-sm font-medium">
+        <button
+          type="button"
+          className="truncate rounded text-start text-sm font-medium"
+          onClick={(event) => {
+            event.stopPropagation();
+            onSelect();
+          }}
+          aria-pressed={selected}
+        >
           {index + 1}. {tool?.name ?? step.toolId}
-        </span>
+        </button>
         <div className="flex items-center gap-0.5">
           <button
             type="button"

apps/geolibre-desktop/src/i18n/locales/ar.json

@@ -4316,6 +4316,7 @@
       "importPipeline": "استيراد خط الأنابيب",
       "exportPipeline": "تصدير خط الأنابيب",
       "stepKindTransform": "تحويل",
+      "canvasEmpty": "لا توجد خطوات بعد — أضف خطوة لبناء سير العمل.",
       "inputPreviousStep": "الإدخال: → ناتج الخطوة السابقة",
       "unknownTool": "أداة غير معروفة \"{{id}}\"",
       "noParameters": "لا توجد معاملات."

apps/geolibre-desktop/src/i18n/locales/de.json

@@ -4049,6 +4049,7 @@
       "importPipeline": "Pipeline importieren",
       "exportPipeline": "Pipeline exportieren",
       "stepKindTransform": "Transformation",
+      "canvasEmpty": "Noch keine Schritte — fügen Sie einen hinzu, um den Arbeitsablauf aufzubauen.",
       "inputPreviousStep": "Eingabe: ← Ausgabe des vorherigen Schritts",
       "unknownTool": "Unbekanntes Werkzeug „{{id}}“",
       "noParameters": "Keine Parameter."

apps/geolibre-desktop/src/i18n/locales/en.json

@@ -4059,6 +4059,7 @@
       "importPipeline": "Import pipeline",
       "exportPipeline": "Export pipeline",
       "stepKindTransform": "Transform",
+      "canvasEmpty": "No steps yet — add one to build the workflow.",
       "inputPreviousStep": "Input: ← previous step output",
       "unknownTool": "Unknown tool \"{{id}}\"",
       "noParameters": "No parameters."

apps/geolibre-desktop/src/i18n/locales/es.json

@@ -4049,6 +4049,7 @@
       "importPipeline": "Importar canalización",
       "exportPipeline": "Exportar canalización",
       "stepKindTransform": "Transformación",
+      "canvasEmpty": "Aún no hay pasos: añade uno para crear el flujo de trabajo.",
       "inputPreviousStep": "Entrada: ← salida del paso anterior",
       "unknownTool": "Herramienta desconocida «{{id}}»",
       "noParameters": "Sin parámetros."

apps/geolibre-desktop/src/i18n/locales/fa.json

@@ -4049,6 +4049,7 @@
       "importPipeline": "درون‌ریزی خط لوله",
       "exportPipeline": "برون‌بری خط لوله",
       "stepKindTransform": "تبدیل",
+      "canvasEmpty": "هنوز مرحله‌ای وجود ندارد — برای ساخت گردش کار یکی اضافه کنید.",
       "inputPreviousStep": "ورودی: → خروجی گام پیشین",
       "unknownTool": "ابزار ناشناختهٔ «{{id}}»",
       "noParameters": "بدون پارامتر."

apps/geolibre-desktop/src/i18n/locales/fr.json

@@ -4049,6 +4049,7 @@
       "importPipeline": "Importer le pipeline",
       "exportPipeline": "Exporter le pipeline",
       "stepKindTransform": "Transformation",
+      "canvasEmpty": "Aucune étape pour l'instant — ajoutez-en une pour créer le flux de travail.",
       "inputPreviousStep": "Entrée : ← sortie de l'étape précédente",
       "unknownTool": "Outil inconnu « {{id}} »",
       "noParameters": "Aucun paramètre."

apps/geolibre-desktop/src/i18n/locales/hi.json

@@ -4049,6 +4049,7 @@
       "importPipeline": "पाइपलाइन आयात करें",
       "exportPipeline": "पाइपलाइन निर्यात करें",
       "stepKindTransform": "रूपांतरण",
+      "canvasEmpty": "अभी कोई चरण नहीं — वर्कफ़्लो बनाने के लिए एक जोड़ें।",
       "inputPreviousStep": "इनपुट: ← पिछले चरण का आउटपुट",
       "unknownTool": "अज्ञात टूल \"{{id}}\"",
       "noParameters": "कोई पैरामीटर नहीं।"

apps/geolibre-desktop/src/i18n/locales/id.json

@@ -3982,6 +3982,7 @@
       "importPipeline": "Impor pipeline",
       "exportPipeline": "Ekspor pipeline",
       "stepKindTransform": "Transformasi",
+      "canvasEmpty": "Belum ada langkah — tambahkan satu untuk membangun alur kerja.",
       "inputPreviousStep": "Masukan: ← keluaran langkah sebelumnya",
       "unknownTool": "Alat tidak dikenal \"{{id}}\"",
       "noParameters": "Tidak ada parameter."

apps/geolibre-desktop/src/i18n/locales/it.json

@@ -4049,6 +4049,7 @@
       "importPipeline": "Importa pipeline",
       "exportPipeline": "Esporta pipeline",
       "stepKindTransform": "Trasformazione",
+      "canvasEmpty": "Nessun passaggio — aggiungine uno per creare il flusso di lavoro.",
       "inputPreviousStep": "Input: ← output del passaggio precedente",
       "unknownTool": "Strumento sconosciuto «{{id}}»",
       "noParameters": "Nessun parametro."