feat: batch favorites endpoint + frontend dedup fixes

Backend:
- Add POST /api/favorites/batch endpoint (single multi-row INSERT)
- Add BatchFavoritesResult/BatchFavoritesStats DTOs
- Add batch methods to ports, service, PG repository
- Transaction-based insert with ON CONFLICT DO NOTHING, chunking at 5000

Frontend:
- Rewrite batchFavorites() to single API call (40 requests → 1)
- Add _replaceCacheFromResponse() to avoid extra GET round-trip
- Centralize formatFileSize, isTextViewable, formatDateTime, formatDateShort
- Remove duplicate icon mapping from app.js
- Fix inconsistent quota defaults (10GB everywhere)

static/js/recent.js

@@ -158,9 +158,7 @@ const recent = {
                 : (window.i18n ? window.i18n.t('files.file_types.document') : 'Document'));
 
         const fileSize = isFolder ? '--' : (item.size_formatted || (window.formatFileSize ? window.formatFileSize(item.item_size || 0) : '0 B'));
-        const accessedDate = new Date(item.accessed_at);
-        const formattedDate = accessedDate.toLocaleDateString() + ' ' +
-            accessedDate.toLocaleTimeString([], { hour: '2-digit', minute: '2-digit' });
+        const formattedDate = window.formatDateTime(item.accessed_at);
 
         // Click handler
         const onClick = () => {