Keep the colleague's microbu-esp32c5 tree in this repository

obu-firmware builds against vanetza-idf from microbu-esp32c5/external, but
that tree was gitignored, so a clone of this repository could not build the
firmware it ships. It is now committed here as ordinary files in its own
folder, microbu-esp32c5/: the colleague's commit cf4b99f plus the V2X2MAP
bridge's signature verification (--trust) used on the bench. Nothing is
fetched from or pushed to the colleague's repository; this repository and
its remotes carry everything. The folder's own .gitignore keeps build output,
downloaded components and private key material out, as it did there; the
committed file set is identical to that repository's tracked files.

The ESP32-C5 is still flashed from obu-firmware/, which only takes
vanetza-idf from microbu-esp32c5/, so the two stay separate folders.
FLASHING.md says how to take a newer version of the colleague's tree (copy
it over the folder, rebuild, test, commit).

microbu-esp32c5/firmware/main/board_controls.cpp

@@ -0,0 +1,59 @@
+#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() {
+    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)");
+}
+
+void BoardControls::apply_led_state() {
+    // 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);
+}
+
+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