feat(sub): per-inbound sort order for subscription links

Add a subSortIndex field to inbounds that controls the order of links
in subscription output only: the raw sub body, the HTML sub page, and
the JSON/Clash formats (all served from the same query). Lower values
come first; ties keep id order. The panel inbound list is unaffected.

The value is editable in the inbound form next to the share-address
fields, propagates to nodes via wireInbound, and follows the usual
node-sync rules (copied on import, mirrored while not dirty, never a
structural change).

Rescoped from #5214 by @Ponywka.

frontend/src/pages/inbounds/form/InboundFormModal.tsx

@@ -575,6 +575,14 @@ export default function InboundFormModal({
         </Form.Item>
       )}
 
+      <Form.Item
+        name="subSortIndex"
+        label={t('pages.inbounds.form.subSortIndex')}
+        extra={t('pages.inbounds.form.subSortIndexHelp')}
+      >
+        <InputNumber min={1} />
+      </Form.Item>
+
       <Form.Item
         name="port"
         label={t('pages.inbounds.port')}