feat: enforce email null when deleted is set (#10680)

## About the changes
When deleting a user we set the email to null and deleted_at to the
current date, there's no case where email is set and deleted_at is also
set.

We found some situations where this happens, specifically when SAML and
SCIM are used in conjunction

src/lib/features/instance-stats/getLicensedUsers.e2e.test.ts

@@ -16,7 +16,7 @@ const mockUser = (deletedDaysAgo: number | null, uniqueId: number) => {
             ? new Date(Date.now() - deletedDaysAgo * 24 * 60 * 60 * 1000)
             : null;
     return {
-        email: `${uniqueId}.user@example.com`,
+        email: deletedAt === null ? `${uniqueId}.user@example.com` : null,
         email_hash: `${uniqueId}.user@example.com`,
         deleted_at: deletedAt,
     };

src/migrations/20250922151744-amend-deleted-at.js

@@ -0,0 +1,25 @@
+
+exports.up = (db, callback) => {
+    db.runSql(
+        `
+        UPDATE users
+        SET deleted_at = NULL
+        WHERE deleted_at IS NOT NULL and length(email) > 0;
+
+        ALTER TABLE users
+        ADD CONSTRAINT deleted_at_requires_email_null
+        CHECK (deleted_at IS NULL OR email IS NULL);
+        `,
+        callback,
+    );
+};
+
+exports.down = (db, callback) => {
+    db.runSql(
+        `
+        ALTER TABLE users
+        DROP CONSTRAINT deleted_at_requires_email_null;
+        `,
+        callback,
+    );
+};