- admin_safe_set_is_admin: short-circuit when target.is_admin == value,
before writing audit. PATCH {is_admin: true} on someone already admin
previously wrote a misleading "promote_user" row even though the UPDATE
was a no-op.
- list_chapters (/admin/mangas/:id/chapters): explicit exists() check on
manga_id, returns 404 instead of 200 [] for a typo'd / deleted manga.
- ChapterSyncState priority: the Failed branch now requires page_count = 0,
so a chapter with pages on disk AND a historical dead job (from a
re-download attempt that crashed) stays Synced. The old order
contradicted Synced's documented "downloaded at some point" contract.
Doc comments updated alongside the SQL.
Three new regression tests pin the behaviour.
aa2159ca06