feat(codex): expose official routing and restore the built-in provider

Let users switch between the built-in OpenAI provider and third-party Codex providers directly from the provider panel while takeover mode remains active.

Centralize the frontend capability predicate so only the fixed codex-official seed receives native-login routing support, and keep copied UUID-based official entries clearly marked as unsupported.

Add an idempotent backend command that recreates the deleted official seed, wire it into the add-provider flow, refresh localized guidance, and add mutation and provider-action regression coverage.

src-tauri/src/commands/provider.rs

@@ -231,6 +231,14 @@ pub fn ensure_claude_desktop_official_provider(state: State<'_, AppState>) -> Re
         .map_err(|e| e.to_string())
 }
 
+#[tauri::command]
+pub fn ensure_codex_official_provider(state: State<'_, AppState>) -> Result<bool, String> {
+    state
+        .db
+        .ensure_official_seed_by_id(crate::database::CODEX_OFFICIAL_PROVIDER_ID, AppType::Codex)
+        .map_err(|e| e.to_string())
+}
+
 fn claude_provider_models_are_claude_safe(provider: &Provider) -> bool {
     let Some(env) = provider
         .settings_config