[codex] Track plugin install and import telemetry failures (#28731)

## Summary
- Track plugin install failures through the unified
`codex_plugin_install_failed` event for local installs, remote install
preflight failures, bundle failures, and remote catalog/backend
failures.
- Send classified `error_type` values in plugin install failure
analytics instead of raw error strings.
- Stop sending raw external-agent import errors in analytics while
preserving raw failure details in app-facing import
notifications/history.
- Keep raw plugin/migration diagnostics in `tracing::warn!` logs.
- Keep remote failure plugin names as the existing local placeholder
(`unknown`) and remove the extra telemetry plugin-name override.
- Change `ExternalAgentConfigImportParams.source` from a generated enum
to `string | null`, with legacy `claudeCode` / `claudeCowork` inputs
normalized to existing analytics values.

## Testing

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

@@ -651,7 +651,7 @@ pub struct ExternalAgentConfigDetectResponse {
 #[serde(rename_all = "camelCase")]
 #[ts(export_to = "v2/")]
 pub struct ExternalAgentConfigDetectParams {
-    /// If true, include detection under the user's home (~/.claude, ~/.codex, etc.).
+    /// If true, include detection under the user's home directory.
     #[serde(default, skip_serializing_if = "std::ops::Not::not")]
     pub include_home: bool,
     /// Zero or more working directories to include for repo-scoped detection.
@@ -664,6 +664,9 @@ pub struct ExternalAgentConfigDetectParams {
 #[ts(export_to = "v2/")]
 pub struct ExternalAgentConfigImportParams {
     pub migration_items: Vec<ExternalAgentConfigMigrationItem>,
+    /// Source product that produced the migration items. Missing means unspecified.
+    #[ts(optional = nullable)]
+    pub source: Option<String>,
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]

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

@@ -376,6 +376,7 @@ fn external_agent_config_import_params_accept_legacy_plugin_details() {
                     ..Default::default()
                 }),
             }],
+            source: None,
         }
     );
 }