Add batch upload configure modal and settings mapping utilities.

Users configure share mode, expiry, and max views before upload; batch summary confirms choices above the queue.

frontend/src/utils/upload/resolveUploadBatchExpiresAt.ts

@@ -0,0 +1,20 @@
+import dayjs from 'dayjs';
+import type { UploadExpiryPreset } from '@/types/upload/UploadExpiryPreset';
+import type { UploadExpiryOffset } from '@/types/upload/UploadExpiryOffset';
+
+const EXPIRY_OFFSET: Record<Exclude<UploadExpiryPreset, 'never'>, UploadExpiryOffset> = {
+    '1h': { amount: 1, unit: 'hour' },
+    '24h': { amount: 24, unit: 'hour' },
+    '7d': { amount: 7, unit: 'day' },
+    '30d': { amount: 30, unit: 'day' }
+};
+
+export const resolveUploadBatchExpiresAt = (preset: UploadExpiryPreset): string | null => {
+    if (preset === 'never') {
+        return null;
+    }
+
+    const { amount, unit } = EXPIRY_OFFSET[preset];
+
+    return dayjs().add(amount, unit).toISOString();
+};