feat: Expose plugin versions and gate plugin sharing (#22397)

- Adds localVersion to plugin summaries and remoteVersion to share
context, including generated API schemas.
- Hydrates local and remote plugin versions from manifests and remote
release metadata.
- Adds default-on plugin_sharing gate for shared-with-me listing and
plugin/share/save, with disabled-path errors
    and focused coverage.

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json

@@ -12289,6 +12289,14 @@
           "remotePluginId": {
             "type": "string"
           },
+          "remoteVersion": {
+            "default": null,
+            "description": "Version of the remote shared plugin release when available.",
+            "type": [
+              "string",
+              "null"
+            ]
+          },
           "sharePrincipals": {
             "items": {
               "$ref": "#/definitions/v2/PluginSharePrincipal"
@@ -12705,6 +12713,14 @@
             },
             "type": "array"
           },
+          "localVersion": {
+            "default": null,
+            "description": "Version of the locally materialized plugin package when available.",
+            "type": [
+              "string",
+              "null"
+            ]
+          },
           "name": {
             "type": "string"
           },