main independently shipped 021_hashtag_counts_respect_bans and
022_client_upload_idempotency. sqlx::migrate! embeds ./migrations and refuses two
files per version, so these three had to move before the branch could merge at all.
Contents are untouched — only the version prefixes change. Renumbering (rather than
renumbering main's) is the safe direction: main is already deployed, so its 021 and
022 are applied in production and their versions are now immutable.
