feat(domains): add Aliases count column

Same account-alias-count-column deviation already used on Accounts,
Groups, and Mailing Lists, extended to x:Domain: adds a synthetic
aliasCount column resolved from the real aliases property (a `set` of
alias domain names here, vs. an objectList elsewhere — same id-keyed
wire format, so the existing generic COUNT_COLUMN_SOURCES handling
needed no changes).

Verified in the running dev server: the column renders correctly
alongside the domain's existing Enabled/Certificate/DNS columns.

src/lib/domainColumns.ts

@@ -0,0 +1,29 @@
+/*
+ * SPDX-FileCopyrightText: 2020 Stalwart Labs LLC <hello@stalw.art>
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
+ */
+
+import type { Schema } from '@/types/schema';
+
+/**
+ * SCHEMA-DEVIATION: account-alias-count-column (see SCHEMA_DEVIATIONS.md)
+ *
+ * The Domains list doesn't expose alias-domain count as a column, only
+ * the full `aliases` set on the detail view. Adds the same synthetic
+ * `aliasCount` column already used on Accounts/Groups/Mailing Lists —
+ * DynamicList's generic count-column handling picks it up with no
+ * further wiring.
+ */
+export function withDomainColumns(schema: Schema): Schema {
+  const list = schema.lists['x:Domain'];
+  if (!list) return schema;
+
+  return {
+    ...schema,
+    lists: {
+      ...schema.lists,
+      'x:Domain': { ...list, columns: [...list.columns, { name: 'aliasCount', label: 'Aliases' }] },
+    },
+  };
+}