Add migration to deduplicate connectors and enforce uniqueness

Delete duplicate connectors per (organization_id, provider), keeping the
oldest one, then add a unique index to prevent future duplicates.

Signed-off-by: Sacha Al Himdani <sacha@getprobo.com>

pkg/coredata/migrations/20260414T125046Z.sql

@@ -0,0 +1,42 @@
+-- Copyright (c) 2026 Probo Inc <hello@getprobo.com>.
+--
+-- Permission to use, copy, modify, and/or distribute this software for any
+-- purpose with or without fee is hereby granted, provided that the above
+-- copyright notice and this permission notice appear in all copies.
+--
+-- THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+-- REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+-- AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+-- INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+-- LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+-- OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+-- PERFORMANCE OF THIS SOFTWARE.
+
+-- Deduplicate connectors per (organization_id, provider), keeping the oldest one.
+-- Temporarily switch access_sources FK to CASCADE for cleanup, then restore RESTRICT.
+
+-- Swap FK to CASCADE so deleting duplicate connectors cascades to their access_sources.
+ALTER TABLE access_sources DROP CONSTRAINT access_sources_connector_id_fkey;
+ALTER TABLE access_sources ADD CONSTRAINT access_sources_connector_id_fkey
+    FOREIGN KEY (connector_id) REFERENCES connectors(id) ON DELETE CASCADE;
+
+-- Delete the duplicate connectors (access_sources will cascade).
+DELETE FROM connectors
+WHERE id IN (
+    SELECT id FROM (
+        SELECT id,
+               ROW_NUMBER() OVER (
+                   PARTITION BY organization_id, provider
+                   ORDER BY created_at ASC
+               ) AS rn
+        FROM connectors
+    ) ranked
+    WHERE rn > 1
+);
+
+-- Restore FK to RESTRICT.
+ALTER TABLE access_sources DROP CONSTRAINT access_sources_connector_id_fkey;
+ALTER TABLE access_sources ADD CONSTRAINT access_sources_connector_id_fkey
+    FOREIGN KEY (connector_id) REFERENCES connectors(id);
+
+CREATE UNIQUE INDEX idx_connectors_organization_id_provider ON connectors (organization_id, provider);