[plugins] Inject remote_plugin_id into install elicitations (#26409)

Summary
- Propagate cached remote plugin IDs through Codex plugin discovery.
- Inject `remote_plugin_id` and connector IDs into
`request_plugin_install` elicitation `_meta` from the resolved plugin.
- Keep the remote plugin ID out of the model-facing tool schema,
arguments, and result.

Validation
- `just test -p codex-tools`
- `just test -p codex-core-plugins`
- `just test -p codex-core
list_tool_suggest_discoverable_plugins_includes_cached_remote_global_plugins`
- `just fix -p codex-tools`
- `just fix -p codex-core-plugins`
- `just fix -p codex-core`
- `git diff --check`
- `just test -p codex-core` was also attempted: 2,581 passed, 55 failed,
and 1 timed out across unrelated sandbox/environment-sensitive
integration tests.

codex-rs/core/src/plugins/discoverable.rs

@@ -41,6 +41,7 @@ pub(crate) async fn list_tool_suggest_discoverable_plugins(
                 .into_iter()
                 .map(|plugin| DiscoverablePluginInfo {
                     id: plugin.id,
+                    remote_plugin_id: plugin.remote_plugin_id,
                     name: plugin.name,
                     description: plugin.description,
                     has_skills: plugin.has_skills,

codex-rs/core/src/plugins/discoverable_tests.rs

@@ -393,6 +393,7 @@ remote_plugin = true
         remote_plugins,
         vec![DiscoverablePluginInfo {
             id: "github@openai-curated-remote".to_string(),
+            remote_plugin_id: Some("plugins~Plugin_remote_github".to_string()),
             name: "Remote GitHub".to_string(),
             description: Some("Remote GitHub short".to_string()),
             has_skills: true,
@@ -680,6 +681,7 @@ async fn list_tool_suggest_discoverable_plugins_normalizes_description() {
         discoverable_plugins,
         vec![DiscoverablePluginInfo {
             id: "slack@openai-curated".to_string(),
+            remote_plugin_id: None,
             name: "slack".to_string(),
             description: Some("Plugin with extra spacing".to_string()),
             has_skills: true,
@@ -816,6 +818,7 @@ discoverables = [{ type = "plugin", id = "sample@openai-curated" }]
         discoverable_plugins,
         vec![DiscoverablePluginInfo {
             id: "sample@openai-curated".to_string(),
+            remote_plugin_id: None,
             name: "sample".to_string(),
             description: Some(
                 "Plugin that includes skills, MCP servers, and app connectors".to_string(),