ESP-IDF public headers (clean-room)

This directory holds headers that mimic the shape of ESP-IDF public API (esp_log.h, esp_err.h, esp_event.h, esp_timer.h, driver/gpio.h, ...).

Rules:

1. Clean-room only. No file in this tree is copied or derived from the ESP-IDF source tree. Each header is re-authored from the ESP-IDF public API reference documentation, using only the API signatures, enums and struct layouts required for binary/source compatibility with ESP-IDF example applications.
2. Baseline version. Header shape targets the ESP-IDF version declared in vsf_espidf_cfg.h via VSF_ESPIDF_CFG_VERSION_*. When a new baseline is adopted, diff public API changes and update accordingly.
3. Naming. Preserve ESP-IDF public names exactly (esp_err_t, ESP_OK, gpio_set_level, ...). Do not add VSF-specific prefixes to public symbols here; VSF-internal helpers live in ../port/.
4. Layout. Match ESP-IDF include path structure so applications can #include "driver/gpio.h" unchanged.

Planned subdirectories (populated per-module):

• esp_err.h, esp_log.h, esp_check.h, esp_common.h
• esp_event.h, esp_event_base.h
• esp_timer.h
• esp_system.h, esp_mac.h, esp_random.h, esp_chip_info.h
• esp_partition.h, nvs.h, nvs_flash.h
• esp_netif.h, esp_netif_types.h
• esp_http_client.h, esp_http_server.h
• esp_wifi.h, esp_wifi_types.h (stage C, requires external radio)
• freertos/FreeRTOS.h and friends (forwarders to VSF FreeRTOS compat)
• driver/gptimer.h (present)
• driver/gpio.h (present)
• driver/uart.h (present)
• driver/i2c_master.h, driver/spi_master.h, driver/ledc.h, driver/adc.h (pending)
• hal/gpio_types.h, hal/uart_types.h, ...