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FLASHING.md says how to take a newer version of the colleague's tree (copy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/external/vanetza-idf/examples/esp_idf/main/CMakeLists.txt

@@ -0,0 +1,2 @@
+idf_component_register(SRCS "main.cpp" REQUIRES vanetza-idf esp_timer)
+target_compile_features(${COMPONENT_LIB} PRIVATE cxx_std_17)

microbu-esp32c5/external/vanetza-idf/examples/esp_idf/main/main.cpp

@@ -0,0 +1,31 @@
+#include <vanetza_idf/access.hpp>
+#include <esp_log.h>
+#if VIDF_NETWORK
+#include <vanetza_idf/stack.hpp>
+#endif
+
+/** Replace this adapter with a hardware driver or test lower port. No radio is
+ * enabled by this integration example. A non-existent device rejects requests.
+ */
+class ExampleAccess : public vanetza_idf::Access {
+public:
+    vanetza_idf::Result request(vanetza_idf::AlDataRequest) override {
+        return vanetza_idf::Result::unsupported;
+    }
+};
+
+extern "C" void app_main() {
+    ExampleAccess access;
+#if VIDF_NETWORK
+    vanetza::ManualRuntime runtime;
+    vanetza_idf::StackConfig config;
+    config.mib.vanetzaDisableBeaconing = true;
+    vanetza_idf::Stack stack(config, runtime, access);
+    ESP_LOGI("vanetza-idf", "Network profile ready; inject position, time, security and Access adapter");
+    // The application event loop owns stack lifetime. In production, keep this
+    // object alive while processing queued sensor, receive and timer events.
+#else
+    vanetza_idf::AccessStack stack(access);
+    ESP_LOGI("vanetza-idf", "Access profile ready; inject AL_DATA.request primitives");
+#endif
+}