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/schemas/forms/inbound-form.ts

@@ -39,6 +39,7 @@ export const InboundDbFieldsSchema = z.object({
   nodeId: z.number().int().nullable().optional(),
   shareAddrStrategy: ShareAddrStrategySchema.default('node'),
   shareAddr: z.string().default(''),
+  subSortIndex: z.number().int().min(1).default(1),
 });
 export type InboundDbFields = z.infer<typeof InboundDbFieldsSchema>;