Add deep sleep options and UI strings

Introduce new deep-sleep related settings to DeviceConfig (deep_sleep_stay_awake_switch, deep_sleep_stay_awake_entity_id, deep_sleep_firmware_guard) and wire them into the model's loader with sensible defaults (stay-awake entity default: "input_boolean.esphome_stay_awake"). Also add strings.json to provide config/option UI text (setup title/description, single-instance abort, and options including "show_in_sidebar").

Author: koosoli