fix(sub): prevent default profile page URL disclosure (#6538)

* fix(sub): prevent default profile page URL disclosure

Add explicit none, builtin, and custom profile page modes.
Preserve existing custom URLs and warn before exposing the built-in page.
Cover mode selection, legacy settings, and subscription response headers.

* fix(subscription): add profile page link options and upgrade notes

frontend/public/openapi.json

@@ -395,6 +395,9 @@
             "minimum": 1,
             "type": "integer"
           },
+          "subProfileMode": {
+            "type": "string"
+          },
           "subProfileUrl": {
             "type": "string"
           },
@@ -618,6 +621,7 @@
           "subListen",
           "subPath",
           "subPort",
+          "subProfileMode",
           "subProfileUrl",
           "subRoutingRules",
           "subShowIdentityOnAllLinks",
@@ -1046,6 +1050,9 @@
             "minimum": 1,
             "type": "integer"
           },
+          "subProfileMode": {
+            "type": "string"
+          },
           "subProfileUrl": {
             "type": "string"
           },
@@ -1277,6 +1284,7 @@
           "subListen",
           "subPath",
           "subPort",
+          "subProfileMode",
           "subProfileUrl",
           "subRoutingRules",
           "subShowIdentityOnAllLinks",