fix(esp-tls): address MR review comments for SE PSA driver

- esp_tls_mbedtls: require cert when PSA-backed server/client key is set
- esp_tls_mbedtls: drop redundant pk_init/x509_crt_init (calloc handles it)
- psa SE driver: copy callbacks/opaque_key by value (no lifetime coupling)
- psa SE driver: replace atomic CAS with simple null check on register
- psa SE driver: use sig_len from sign callback with bounds validation
- psa SE driver: validate pubkey_len returned by export_pubkey callback
- psa SE driver: check hash sub-alg in RSA PKCS1V15 branch of validate_request
- psa SE driver: align secure_element_register_callbacks doc with value-copy impl
- esp_https_server: initialize server_key in HTTPD_SSL_CONFIG_DEFAULT
- mbedtls: move SECURE_ELEMENT_DRIVER_ENABLED to esp_config.h for parity
  with ESP_ECDSA_DRIVER_ENABLED; drop target_compile_definitions
- docs: fix esp_tls_cfg_t -> esp_http_client_config_t cross-reference
- docs: check psa_import_key() status in ESP-TLS PSA example
- hints/error_output: point at CONFIG_MBEDTLS_SECURE_ELEMENT_DRIVER_ENABLED

docs/zh_CN/api-reference/protocols/esp_tls.rst

@@ -255,8 +255,12 @@ ESP-TLS 支持通过 PSA Crypto 不透明驱动接口在 ESP32 系列芯片上
        };
 
        psa_key_id_t psa_key_id;
-       psa_import_key(&key_attr, (const uint8_t *)&opaque_key,
-                      sizeof(opaque_key), &psa_key_id);
+       psa_status_t status = psa_import_key(&key_attr, (const uint8_t *)&opaque_key,
+                                            sizeof(opaque_key), &psa_key_id);
+       if (status != PSA_SUCCESS) {
+           /* 处理错误 - 通常表示安全元件回调未注册或属性无效。 */
+           return;
+       }
 
        /* 配置 ESP-TLS 使用 PSA 密钥 */
        esp_key_config_t key_config = {