Scope document signatures to the major version

A signature applies to a whole major: minor publishes keep it and the
export unions signatures across every minor of the major. The request
guard was scoped to a single minor, so re-requesting on a newer minor
(or twice on the same version) inserted duplicate rows and a signatory
appeared several times on the exported signature page.

Deduplicate by loading any existing signature across the major before
inserting, cancel still-pending requests from prior majors when a new
major is published, and restrict the export to active signatories
(comparing contract end dates against the current date). A migration
collapses the duplicate rows already in the table, preferring a signed
row over a pending one and then the most recent.

Signed-off-by: Bryan Frimin <bryan@probo.com>

pkg/coredata/migrations/20260529T010239Z.sql

@@ -0,0 +1,39 @@
+-- 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.
+
+-- A signature applies to a whole major version: minor publishes keep it and the
+-- export unions signatures across every minor of the major. A signatory must
+-- therefore have at most one signature per (document, major). Historically the
+-- request guard was scoped to a single minor version, so re-requesting on a
+-- newer minor (or twice on the same version) inserted duplicate rows, making a
+-- person appear several times on the exported signature page.
+--
+-- Collapse each (document, major, signatory) group to a single signature,
+-- keeping the same row the application now prefers: a SIGNED signature over a
+-- pending one, then the most recently created.
+WITH ranked AS (
+    SELECT
+        dvs.id,
+        ROW_NUMBER() OVER (
+            PARTITION BY dv.document_id, dv.major, dvs.signed_by_profile_id
+            ORDER BY
+                CASE dvs.state WHEN 'SIGNED' THEN 0 ELSE 1 END,
+                dvs.created_at DESC,
+                dvs.id DESC
+        ) AS rn
+    FROM document_version_signatures dvs
+    INNER JOIN document_versions dv ON dvs.document_version_id = dv.id
+)
+DELETE FROM document_version_signatures
+WHERE id IN (SELECT id FROM ranked WHERE rn > 1);