Adds an `allow_downloads` boolean to `photo_categories` so admins can
have different download policies per category — e.g. preview categories
public, originals client-only. AND's with the event-level `allow_downloads`,
so disabling at either level blocks downloads for that category's photos.
Defaults to true so categories created before migration 135 keep working
without admin intervention.
Credit: 8digit/picpeak@928164b + @751ec75.
### Backend
- **Migration 135**: additive `allow_downloads BOOLEAN NOT NULL DEFAULT true`
on `photo_categories`, hasColumn-guarded + sane down.
- **`adminCategories.js`**: PUT /:id accepts optional `allow_downloads` patch.
- **`gallery.js`**:
- `GET /:slug/photos` returns `allow_downloads` per category AND
`category_allow_downloads` per photo.
- `GET /:slug/download/:photoId` returns 403 when the photo's category
disables downloads.
- `GET /:slug/download-all` LEFT JOINs `photo_categories` and filters
`whereNull(category_id) OR allow_downloads=true OR allow_downloads IS NULL`.
The null check covers pre-migration-135 rows during the upgrade window.
- `POST /:slug/download-selected` same filter pattern.
### Frontend
- **`categories.service.ts`**: `updateCategory()` gains an optional `patch`
argument carrying `{ allow_downloads }`. PhotoCategory interface gains the
optional field.
- **`EventCategoryManager.tsx`**: new toggle button next to the delete X.
Green DownloadCloud icon when downloads are on, plain Download icon when
off. Click toggles via the new mutation; toast confirms.
- **`PhotoLightbox.tsx`**: `photoAllowsDownload = allowDownloads && currentPhoto?.category_allow_downloads !== false`. Hides the download button +
blocks the 'D' keyboard shortcut + early-returns from handleDownload.
- **Types**: Photo interface gains `category_allow_downloads`.
- **i18n**: 5 new EN + DE entries for the toggle button toast + tooltip.
No global-category surface change yet — global categories don't currently
have a UI for the toggle. Admins can still flip the column directly via SQL
or via a future global-categories editor.
### Test plan
- [x] Backend syntax + TS check clean
- [x] ESLint: no new warnings
- [ ] Manual: admin → event detail → categories panel → click DownloadCloud
icon → category flips, toast confirms
- [ ] Manual: gallery (guest) → photo in disabled category → lightbox shows
no download button, 'D' shortcut is a no-op
- [ ] Manual: download-all on a gallery with one disabled category →
ZIP excludes that category's photos
- [ ] Manual: download-selected including a disabled-category photo → 404
(filtered out) and the response carries only the allowed selection
- [ ] Manual: pre-migration-135 category (legacy row with NULL allow_downloads)
→ downloads still work (defaults true via fallback)