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FLASHING.md says how to take a newer version of the colleague's tree (copy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.hpp

@@ -0,0 +1,31 @@
+#pragma once
+
+#include <cstdint>
+
+namespace microbu {
+
+/// XIAO ESP32-C5 active-low user LED: a visual indicator for TX/RX activity.
+class BoardControls {
+public:
+    /// @brief Configures the LED GPIO and sets its idle state.
+    BoardControls();
+
+    enum class LedMode {
+        normal_tx,   // Normally off, pulses on upon frame dissemination
+        inverted_rx  // Normally on, pulses off upon frame reception
+    };
+
+    /// @brief Triggers visual indication (blink on in normal_tx mode, blink off in inverted_rx mode).
+    void blink();
+    /// @brief Updates LED state and checks indication timers; call periodically.
+    void tick();
+
+private:
+    void apply_led_state();
+
+    LedMode mode_ = LedMode::normal_tx;
+    bool pulsing_ = false;
+    std::int64_t pulse_until_us_ = 0;
+};
+
+} // namespace microbu