Add draft and publish workflows for broadcast and sequence emails

.changeset/email-drafts-and-publish.md

@@ -0,0 +1,6 @@
+---
+"sendlit": minor
+"@sendlit/email-blocks": minor
+---
+
+Draft and publish for broadcast and sequence emails. While a broadcast or sequence is active (a running sequence or a scheduled broadcast), `sequences.updateEmail` saves subject and content changes as a draft (the email's `draft`, with `hasUnpublishedChanges` on the email and the sequence) and sends keep using the published version. New methods: `sequences.publishChanges` (with `scope: "in_flight" | "new_entrants"` for sequences), `sequences.discardChanges`, `sequences.emailVersions` and `sequences.restoreEmailVersion`. `@sendlit/email-blocks` adds `draft` and `hasUnpublishedChanges` to its sequence types.

apps/api/drizzle/0031_email_drafts.sql

@@ -0,0 +1,5 @@
+ALTER TABLE "email_content_versions" ADD COLUMN "published_at" timestamp with time zone;--> statement-breakpoint
+ALTER TABLE "ongoing_sequences" ADD COLUMN "pinned_versions" jsonb;--> statement-breakpoint
+ALTER TABLE "sequence_emails" ADD COLUMN "draft_subject" text;--> statement-breakpoint
+ALTER TABLE "sequence_emails" ADD COLUMN "draft_content" jsonb;--> statement-breakpoint
+ALTER TABLE "sequence_emails" ADD COLUMN "draft_updated_at" timestamp with time zone;