feat: Normalize remote plugin summary identities. (#22265)

Makes plugin summaries use config-style plugin@marketplace IDs while
exposing backend remote IDs separately as remotePluginId.

Also fix the consistency issue of REMOTE_SHARED_WITH_ME_MARKETPLACE_NAME

codex-rs/app-server-protocol/schema/json/v2/PluginReadResponse.json

@@ -506,6 +506,13 @@
         "name": {
           "type": "string"
         },
+        "remotePluginId": {
+          "description": "Backend remote plugin identifier when available.",
+          "type": [
+            "string",
+            "null"
+          ]
+        },
         "shareContext": {
           "anyOf": [
             {