Bilibili author-folder collision and subscription-ordering issues

[franklioxygen]

The user reported two separate data-integrity and correctness problems:

1. With Author folders only enabled, different Bilibili videos from the same uploader can have the same title and therefore the same legacy filename. A later video can replace the earlier file. The database may retain multiple video records, but only one set of bytes remains. Template naming does not fully solve the user's workflow because author_folder_only currently does not physically organize non-legacy/template output.
2. Selecting historical subscription order oldest first no longer changes the effective order. Downloads still normally run newest first. The ordering comparator is present, but the enumerator frequently represents missing dates as "00000000". When every date is unknown, a stable sort preserves the source's original newest-first order. Playlist subscription paths also hard-code dateDesc and hide/omit the order control.