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FLASHING.md says how to take a newer version of the colleague's tree (copy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/tools/fuzz-harness/run.cpp

@@ -0,0 +1,42 @@
+#include "router_fuzzing_context.hpp"
+#include <iostream>
+#include <fstream>
+
+vanetza::ByteBuffer readFileIntoBuffer(const std::string &filename)
+{
+    std::ifstream file(filename, std::ios::binary | std::ios::ate);
+    if (!file.is_open()) {
+        std::cerr << "Error opening file: " << filename << std::endl;
+        return {};
+    }
+
+    const std::streamsize size = file.tellg();
+    file.seekg(0, std::ios::beg);
+
+    vanetza::ByteBuffer buffer(size);
+    if (!file.read(reinterpret_cast<char *>(buffer.data()), size)) {
+        std::cerr << "Error reading file: " << filename << std::endl;
+        return {};
+    }
+
+    return buffer;
+}
+
+int main(int argc, char* argv[])
+{
+    if (argc != 2) {
+        std::cerr << "Usage: " << argv[0] << " <filepath>" << std::endl;
+        return 1;
+    }
+
+    const std::string filename = argv[1];
+    vanetza::ByteBuffer buffer = readFileIntoBuffer(filename);
+
+    if (buffer.empty()) {
+        return 1;
+    }
+
+    vanetza::RouterFuzzingContext context;
+    context.indicate(std::move(buffer));
+    return 0;
+}