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/public/openapi.json

@@ -1345,6 +1345,12 @@
           },
           "sniffing": {},
           "streamSettings": {},
+          "subSortIndex": {
+            "description": "1-based sort order of this inbound's links in subscription output only (lower first; ties by id)",
+            "example": 1,
+            "minimum": 1,
+            "type": "integer"
+          },
           "tag": {
             "example": "in-443-tcp",
             "type": "string"
@@ -1385,6 +1391,7 @@
           "shareAddrStrategy",
           "sniffing",
           "streamSettings",
+          "subSortIndex",
           "tag",
           "total",
           "trafficReset",
@@ -2153,6 +2160,7 @@
                       "shareAddrStrategy": "node",
                       "sniffing": null,
                       "streamSettings": null,
+                      "subSortIndex": 1,
                       "tag": "in-443-tcp",
                       "total": 0,
                       "trafficReset": "never",