Sign ITS messages on the ESP32-C5 with vanetza-idf, over USB or BLE

obu-firmware is now a port of the colleague's standalone VRU station
(microbu-esp32c5/firmware, kept beside this repository and gitignored): the
vanetza-idf C-ITS stack with the TS 103 097 security entity, credentials in
NVS, the station-link v1 protocol over the native USB port (frame type 0x10
in the existing 0xAA55 framing) and over a BLE GATT peripheral, and its
ITS-G5 radio adapter. The phone still builds CAM and VAM; the board adds
GeoNetworking/BTP and signs with the provisioned authorization ticket. The
private key never leaves the board. Builds with ESP-IDF 6.0.2 only, which
vanetza-idf pins for the radio's private driver ABI. The previous C firmware
stays on disk unbuilt; a full-flash backup of the bench board is kept in
firmware-backups/ (gitignored).

Changed against the colleague's firmware, marked MicrOBU: in the sources:
- Reception unchanged for the app. vanetza-idf drops what it cannot verify
  (unsigned traffic, every RSU), so each captured frame also goes through the
  previous gn_unwrap.c and reaches the phone as link opcode V2X_RX (0x85),
  whose body is the old SERIAL_MSG_V2X_RX payload.
- Unsigned transmission still possible, with the previous geonet.c header;
  the phone chooses per message.
- Console on UART0 (CH343 port); the native USB port carries only link frames.
- BLE advertising pauses while the USB link is in use: BLE and ITS-G5 share
  one RF front end.
- NVS 80 KB (app at 0x20000). At 24 KB, with Wi-Fi settings the previous
  firmware left behind, the BLE bond could not be stored and the phone had to
  pair on every connection.
- Bench fixes: the radio queue is drained before the first PoTi (no RX and
  ~177 queue drops before); the station loop waited pdMS_TO_TICKS(5) = 0
  ticks at 100 Hz and starved the idle task; the 2.4 KB RX capture buffer is
  off the Wi-Fi task stack; BLE notifications longer than the MTU are dropped
  instead of cut short, MTU 517; serial writes are skipped with no USB host.
- Manual country policy and TX-power read-back from the previous radio setup;
  logs for BLE encryption changes and the number of stored bonds.

Verified on the bench board (COM3) with the phone over USB and BLE: CAM and
VAM, signed and unsigned, go out; reception of the sim car and the RSU's
CAM/SPATEM/MAPEM continues; the board survives app restarts and reconnects.
See docs/06-signed-its-vam-ble.md.

obu-firmware/main/board_controls.cpp

@@ -0,0 +1,65 @@
+#include "board_controls.hpp"
+
+#include <driver/gpio.h>
+#include <esp_log.h>
+#include <esp_timer.h>
+
+namespace microbu {
+namespace {
+const char* TAG = "board";
+constexpr std::int64_t blink_us = CONFIG_MICROBU_TX_LED_BLINK_MS * 1000LL;
+}
+
+BoardControls::BoardControls() {
+#if CONFIG_MICROBU_TX_LED_GPIO < 0
+    ESP_LOGI(TAG, "no activity LED configured");
+#else
+    gpio_config_t led = {};
+    led.pin_bit_mask = 1ULL << CONFIG_MICROBU_TX_LED_GPIO;
+    led.mode = GPIO_MODE_OUTPUT;
+    led.pull_up_en = GPIO_PULLUP_DISABLE;
+    led.pull_down_en = GPIO_PULLDOWN_DISABLE;
+    led.intr_type = GPIO_INTR_DISABLE;
+    ESP_ERROR_CHECK(gpio_config(&led));
+#if CONFIG_MICROBU_LED_INVERTED_RX
+    mode_ = LedMode::inverted_rx;
+#else
+    mode_ = LedMode::normal_tx;
+#endif
+    apply_led_state();
+    ESP_LOGI(TAG, "LED GPIO %d (mode: %s)", CONFIG_MICROBU_TX_LED_GPIO,
+             mode_ == LedMode::inverted_rx ? "inverted_rx (normally ON)" : "normal_tx (normally OFF)");
+#endif
+}
+
+void BoardControls::apply_led_state() {
+#if CONFIG_MICROBU_TX_LED_GPIO >= 0
+    // The XIAO ESP32-C5 user LED is wired active-low (0 = ON, 1 = OFF).
+    // In normal_tx mode: default OFF (1), pulsing ON (0).
+    // In inverted_rx mode: default ON (0), pulsing OFF (1).
+    bool led_illuminated = false;
+    if (mode_ == LedMode::normal_tx) {
+        led_illuminated = pulsing_;
+    } else {
+        led_illuminated = !pulsing_;
+    }
+    gpio_set_level(static_cast<gpio_num_t>(CONFIG_MICROBU_TX_LED_GPIO), led_illuminated ? 0 : 1);
+#endif
+}
+
+void BoardControls::blink() {
+    pulse_until_us_ = esp_timer_get_time() + blink_us;
+    if (!pulsing_) {
+        pulsing_ = true;
+        apply_led_state();
+    }
+}
+
+void BoardControls::tick() {
+    if (pulsing_ && esp_timer_get_time() >= pulse_until_us_) {
+        pulsing_ = false;
+        apply_led_state();
+    }
+}
+
+} // namespace microbu