feat: Add remote plugin fields to plugin API (#17277)

## Summary
Update the plugin API for the new remote plugin model.

The mental model is no longer “keep local plugin state in sync with
remote.” Instead, local and remote plugins are becoming separate
sources. Remote catalog entries can be shown directly from the remote
API before installation; after installation they are still downloaded
into the local cache for execution, but remote installed state will come
from the API and be held in memory rather than being read from config.

• ## API changes
- Remove `forceRemoteSync` from `plugin/list`, `plugin/install`, and
`plugin/uninstall`.
  - Remove `remoteSyncError` from `plugin/list`.
  - Add remote-capable metadata to `plugin/list` / `plugin/read`:
    - nullable `marketplaces[].path`
    - `source: { type: "remote", downloadUrl }`
    - URL asset fields alongside local path fields:
  `composerIconUrl`, `logoUrl`, `screenshotUrls`
  - Make `plugin/read` and `plugin/install` source-compatible:
    - `marketplacePath?: AbsolutePathBuf | null`
    - `remoteMarketplaceName?: string | null`
    - exactly one source is required at runtime

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

@@ -7,19 +7,27 @@
     }
   },
   "properties": {
-    "forceRemoteSync": {
-      "description": "When true, apply the remote plugin change before the local install flow.",
-      "type": "boolean"
-    },
     "marketplacePath": {
-      "$ref": "#/definitions/AbsolutePathBuf"
+      "anyOf": [
+        {
+          "$ref": "#/definitions/AbsolutePathBuf"
+        },
+        {
+          "type": "null"
+        }
+      ]
     },
     "pluginName": {
       "type": "string"
+    },
+    "remoteMarketplaceName": {
+      "type": [
+        "string",
+        "null"
+      ]
     }
   },
   "required": [
-    "marketplacePath",
     "pluginName"
   ],
   "title": "PluginInstallParams",