Expose declared onboarding skills in plugin details (#46544)

## What changed

Add an optional `onboardingSkill` summary to `plugin/read` responses and update the generated schemas, TypeScript types, and Python models.

- Resolve local declarations from `extensions["com.openai"].onboardingSkill`, accepting relative paths with or without `./`. Require the resolved path to stay within the plugin root and match a loaded skill.
- Match remote release metadata's `onboarding_skill_name` against the plugin's skills.
- Return the summary only when the plugin and matching visible skill are enabled; remote plugins must also be available. Otherwise, return `null`.

## Testing

Add parameterized local and remote `plugin/read` tests covering matching, missing, and unmatched declarations, disabled plugins and skills, and unavailable remote plugins.

GitOrigin-RevId: 88cabdfddbecba5efba756617da0cb1ff064bdf7

codex-rs/plugin/src/manifest.rs

@@ -18,6 +18,7 @@ pub struct PluginManifest<Resource> {
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct PluginManifestPaths<Resource> {
     pub skills: Vec<Resource>,
+    pub onboarding_skill: Option<Resource>,
     pub mcp_servers: Option<PluginManifestMcpServers<Resource>>,
     pub apps: Option<Resource>,
     pub hooks: Option<PluginManifestHooks<Resource>>,
@@ -105,6 +106,7 @@ impl<Resource> PluginManifest<Resource> {
         } = self;
         let PluginManifestPaths {
             skills,
+            onboarding_skill,
             mcp_servers,
             apps,
             hooks,
@@ -181,6 +183,7 @@ impl<Resource> PluginManifest<Resource> {
                     .into_iter()
                     .map(&mut map)
                     .collect::<Result<Vec<_>, _>>()?,
+                onboarding_skill: onboarding_skill.map(&mut map).transpose()?,
                 mcp_servers,
                 apps: apps.map(&mut map).transpose()?,
                 hooks,

codex-rs/plugin/src/provider_tests.rs

@@ -43,6 +43,7 @@ fn environment_descriptor_binds_every_manifest_resource() {
         description: None,
         keywords: Vec::new(),
         paths: PluginManifestPaths {
+            onboarding_skill: None,
             skills: vec![path_uri(&skills)],
             mcp_servers: Some(PluginManifestMcpServers::Path(path_uri(&mcp_servers))),
             apps: Some(path_uri(&apps)),
@@ -77,6 +78,7 @@ fn environment_descriptor_binds_every_manifest_resource() {
             description: None,
             keywords: Vec::new(),
             paths: PluginManifestPaths {
+                onboarding_skill: None,
                 skills: vec![resource("executor-1", &skills)],
                 mcp_servers: Some(PluginManifestMcpServers::Path(resource(
                     "executor-1",
@@ -109,6 +111,7 @@ fn environment_descriptor_rejects_resources_outside_package_root() {
         description: None,
         keywords: Vec::new(),
         paths: PluginManifestPaths {
+            onboarding_skill: None,
             skills: Vec::new(),
             mcp_servers: Some(PluginManifestMcpServers::Path(path_uri(&outside))),
             apps: None,