The day-grouped timeline is now the site root (/, /page/N/); the flat
square grid moves to /grid/ (/grid/page/N/). Both are linked from the
profile header, separated by a divider.
Timeline pages pack whole day-groups until they reach the page size,
never splitting a day across a page boundary, so appended pages never
repeat a date heading — the infinite-scroll handler relies on this.
Page size is configurable via -page-size (default 60), threaded through
the Generator and exposed as services.photogallery.pageSize in the
NixOS module.
