Previously syncGroupsForAccount only upserted, so groups removed from
WhatsApp (deleted, bot was kicked, etc.) lingered in the DB.
Now compute the diff: any whatsapp_groups row for this account whose
wa_group_jid is not in the live fetch result is deleted. Skip the delete
sweep when the fetch returns empty — that's more likely transient than
a genuine "every group gone" signal, and we don't want to nuke valid
data on a hiccup.
Return shape gains a `removed` count alongside `synced`.
yiekheng
9062ba7e7f