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/models/dbinbound.ts

@@ -42,6 +42,7 @@ export type DBInboundInit = Partial<{
     nodeId: number | null;
     shareAddrStrategy: string;
     shareAddr: string;
+    subSortIndex: number;
     originNodeGuid: string;
     fallbackParent: FallbackParentRef | null;
 }>;
@@ -88,6 +89,7 @@ export class DBInbound {
     nodeId: number | null;
     shareAddrStrategy: string;
     shareAddr: string;
+    subSortIndex: number;
     originNodeGuid: string;
     fallbackParent: FallbackParentRef | null;
 
@@ -116,6 +118,7 @@ export class DBInbound {
         this.nodeId = null;
         this.shareAddrStrategy = "node";
         this.shareAddr = "";
+        this.subSortIndex = 1;
         this.originNodeGuid = "";
         this.fallbackParent = null;
         if (data == null) {