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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,53 @@
+#pragma once
+
+#include "link_protocol.hpp"
+#include <cstdint>
+#include <functional>
+
+namespace microbu::ble {
+
+using Receiver = std::function<void(link::Bytes)>;
+
+/// @brief A set of counters for tracking BLE message traffic.
+struct Counters {
+    std::uint32_t rx_messages = 0;
+    std::uint32_t tx_messages = 0;
+    std::uint32_t tx_failed = 0;
+    std::uint32_t malformed = 0;
+};
+
+/**
+ * @brief Starts a simple, bonded BLE GATT peripheral on the NimBLE host.
+ * Uses structured ETSI C-ITS Station Service & Characteristics:
+ *   Service:             0000C175-BA5E-4C17-8000-00805F9B34FB
+ *   BTP-DATA.request:    0000C176-BA5E-4C17-8000-00805F9B34FB (Write, Authenticated/Encrypted) 
+ *   BTP-DATA.indication: 0000C177-BA5E-4C17-8000-00805F9B34FB (Notify, Authenticated/Encrypted)
+ *   PoTi Fix Update:     0000C178-BA5E-4C17-8000-00805F9B34FB (Write, Authenticated/Encrypted)
+ *   Station Status:      0000C179-BA5E-4C17-8000-00805F9B34FB (Read / Notify, Authenticated/Encrypted)
+ *   SF-SAP Identity:     0000C17A-BA5E-4C17-8000-00805F9B34FB (Notify, Authenticated/Encrypted)
+ *   Station Configure:   0000C17B-BA5E-4C17-8000-00805F9B34FB (Write, Authenticated/Encrypted)
+ *   Result:              0000C17C-BA5E-4C17-8000-00805F9B34FB (Notify, Authenticated/Encrypted)
+ *
+ * Fixed passkey bonding: 123456.
+ * Single ATT message transmission/reception up to 512 bytes without fragmentation chunk delays.
+ * @param receiver Invoked with each decoded station-link message written by the phone.
+ * @return false if the NimBLE host or GATT service failed to start.
+ */
+bool start(Receiver receiver);
+
+/**
+ * @brief Sends one complete station-link message via GATT notification.
+ * Dispatches immediately without queuing delay.
+ * @param message Encoded station-link message to notify.
+ * @return false if not connected/subscribed or the notification could not be sent.
+ */
+bool write(const link::Bytes& message);
+
+/// @return true if a phone is connected.
+bool connected();
+/// @return true if the phone has subscribed to notifications.
+bool is_subscribed();
+/// @return Current message/error counters.
+Counters counters();
+
+} // namespace microbu::ble