B6: SPA navigation after case creation (useNavigate instead of window.location.href)

B7: stop AdminDashboard refetching the case list on selection change

selectedCaseId was both read and written inside the list-loading effect and
listed in its deps, causing a second fetch on first render and after every
filter reset. Auto-select now uses a functional state update, so the effect
no longer depends on selectedCaseId; editForm stays in sync via the existing
selectedCase effect.

frontend/src/pages/AdminDashboard.jsx

@@ -76,11 +76,16 @@ function AdminDashboard() {
           throw new Error(`Не удалось загрузить список кейсов (${response.status})`);
         }
         const payload = await response.json();
-        setCases(payload.items || []);
+        const items = payload.items || [];
+        setCases(items);
         setTotal(payload.total || 0);
-        if ((payload.items || []).length && !selectedCaseId) {
-          setSelectedCaseId(payload.items[0].id);
-          setEditForm(payload.items[0]);
+        // Auto-select the first row only when nothing is selected yet.
+        // Functional update so this effect does not have to read (and depend
+        // on) selectedCaseId — depending on it caused a second fetch on first
+        // render and after every filter reset. editForm is kept in sync by the
+        // selectedCase effect below.
+        if (items.length) {
+          setSelectedCaseId((current) => current || items[0].id);
         }
       } catch (err) {
         if (err.name !== 'AbortError') {
@@ -93,7 +98,7 @@ function AdminDashboard() {
 
     loadCases();
     return () => controller.abort();
-  }, [filters.ageMax, filters.ageMin, filters.status, page, selectedCaseId]);
+  }, [filters.ageMax, filters.ageMin, filters.status, page]);
 
   useEffect(() => {
     const controller = new AbortController();