Expose workspace plugin publish capability (#35254)

## What changed

- Add nullable `canPublishToWorkspace` metadata to plugin share contexts and `plugin/share/save` responses.
- Preserve the remote capability through catalog parsing and app-server responses so clients can decide whether to offer workspace-directory publishing.
- Document that clients should fail closed when the capability is unavailable.

## Testing

- Cover remote catalog parsing, share-save response propagation, and protocol serialization.

GitOrigin-RevId: b0346b3b330169838f800dfdf21dfa5db1a47f4d

codex-rs/app-server-protocol/src/protocol/v2/plugin.rs

@@ -254,6 +254,8 @@ pub struct PluginShareSaveParams {
 pub struct PluginShareSaveResponse {
     pub remote_plugin_id: String,
     pub share_url: String,
+    #[serde(default)]
+    pub can_publish_to_workspace: Option<bool>,
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
@@ -662,6 +664,8 @@ pub struct PluginShareContext {
     pub creator_account_user_id: Option<String>,
     pub creator_name: Option<String>,
     pub share_principals: Option<Vec<PluginSharePrincipal>>,
+    #[serde(default)]
+    pub can_publish_to_workspace: Option<bool>,
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]