refactor: add table primitive and migrations by date; feat: add mcp connectors

backend/migrations/20260428_workflow_shares_unique.sql

@@ -0,0 +1,28 @@
+-- Migration date: 2026-04-28
+
+-- Migration: enforce one share row per (workflow, recipient email) so
+-- re-sharing to the same person updates the existing row instead of
+-- creating duplicates. Without this, DELETE only removes one of N copies
+-- and the recipient retains access after the owner thinks they revoked.
+
+-- Collapse any existing duplicates first, keeping the most recent row.
+delete from public.workflow_shares a
+using public.workflow_shares b
+where a.workflow_id = b.workflow_id
+  and a.shared_with_email = b.shared_with_email
+  and a.created_at < b.created_at;
+
+-- Add the unique constraint only if it is not already present (ADD CONSTRAINT
+-- has no IF NOT EXISTS form, so re-running the bare statement would error).
+do $$
+begin
+  if not exists (
+    select 1 from pg_constraint
+    where conname = 'workflow_shares_workflow_email_unique'
+      and conrelid = 'public.workflow_shares'::regclass
+  ) then
+    alter table public.workflow_shares
+        add constraint workflow_shares_workflow_email_unique
+        unique (workflow_id, shared_with_email);
+  end if;
+end $$;