feat: data export — CSV export for tasks, users, activities

- Backend: GET /api/export/{tasks,users,activities}?month=YYYY-MM
- Frontend: Export panel on Reports page (CEO/CTO/Manager only)
- API: apiExportCsv helper for browser download

src/api.ts

@@ -48,6 +48,21 @@ export async function apiDeleteUser(id: string) {
     });
 }
 
+export async function apiExportCsv(type: 'tasks' | 'users' | 'activities', month?: string) {
+    const params = month ? `?month=${month}` : '';
+    const res = await fetch(`${API_BASE}/export/${type}${params}`);
+    if (!res.ok) throw new Error('Export failed');
+    const blob = await res.blob();
+    const url = URL.createObjectURL(blob);
+    const a = document.createElement('a');
+    a.href = url;
+    a.download = month ? `${type}_${month}.csv` : `${type}_all.csv`;
+    document.body.appendChild(a);
+    a.click();
+    document.body.removeChild(a);
+    URL.revokeObjectURL(url);
+}
+
 // Tasks
 export async function apiFetchTasks() {
     return request('/tasks');