Emit analytics for remote plugin installs (#20267)

## Summary

- emit `codex_plugin_installed` after a remote plugin install succeeds
- keep local installs unchanged, but let remote installs override the
analytics `plugin_id` with the backend remote plugin id
(`plugins~Plugin_...`)
- preserve the local/display identity in `plugin_name` and
`marketplace_name`, plus capability metadata from the installed bundle
- add regression coverage for local install analytics, remote install
analytics, and analytics id override serialization

## Testing

- `just fmt`
- `cargo test -p codex-analytics`
- `cargo test -p codex-app-server`

codex-rs/plugin/src/lib.rs

@@ -42,6 +42,9 @@ pub struct PluginHookSource {
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct PluginTelemetryMetadata {
     pub plugin_id: PluginId,
+    /// Optional backend identifier for remote plugins, used when analytics
+    /// should report the remote id instead of the local plugin cache id.
+    pub remote_plugin_id: Option<String>,
     pub capability_summary: Option<PluginCapabilitySummary>,
 }
 
@@ -49,6 +52,7 @@ impl PluginTelemetryMetadata {
     pub fn from_plugin_id(plugin_id: &PluginId) -> Self {
         Self {
             plugin_id: plugin_id.clone(),
+            remote_plugin_id: None,
             capability_summary: None,
         }
     }
@@ -60,6 +64,7 @@ impl PluginCapabilitySummary {
             .ok()
             .map(|plugin_id| PluginTelemetryMetadata {
                 plugin_id,
+                remote_plugin_id: None,
                 capability_summary: Some(self.clone()),
             })
     }