feat: proširi prikaz dizalice i vlasnika u zadacima

Dodaj detalje dizalice (proizvođač, model i SN) te vlasnika u modal radnog zadatka i kalendar zadataka, uz zajednički frontend helper za DRY prikaz.

Proširi Task API serializer dodatnim poljima za prikaz dizalice/vlasnika i ažuriraj testove serializera za nova izlazna polja.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

frontend/src/lib/taskCraneDisplay.js

@@ -0,0 +1,35 @@
+function normalizeText(value) {
+    const text = String(value || '').trim();
+    return text || '';
+}
+
+export function getTaskCraneKind(task) {
+    const make = normalizeText(task?.vehicle_make);
+    const model = normalizeText(task?.vehicle_model);
+    const kind = [make, model].filter(Boolean).join(' ').trim();
+    return kind || '-';
+}
+
+export function getTaskCraneSerial(task) {
+    const serial = normalizeText(task?.crane_serial_number);
+    return serial || '-';
+}
+
+export function getTaskCraneOwner(task) {
+    return normalizeText(task?.vehicle_owner_name) || '-';
+}
+
+export function getTaskCraneDisplay(task) {
+    const kind = getTaskCraneKind(task);
+    const serial = getTaskCraneSerial(task);
+    if (kind !== '-' && serial !== '-') {
+        return `${kind} (SN ${serial})`;
+    }
+    if (kind !== '-') {
+        return kind;
+    }
+    if (serial !== '-') {
+        return `SN ${serial}`;
+    }
+    return normalizeText(task?.vehicle_registration) || '-';
+}