Keep vanetza-idf in obu-firmware, so a plain clone builds the firmware

obu-firmware builds against the vanetza-idf C-ITS library, which until now
came from the colleague's microbu-esp32c5 tree beside the repository and was
not tracked here, so a clone of this repository could not build the firmware
it ships. The library alone is now part of obu-firmware, as
obu-firmware/external/vanetza-idf: their external/vanetza-idf at commit
cf4b99f, unchanged (9775 files; see its PROVENANCE.md). CMake takes it from
there by default; -DVANETZA_IDF_DIR still points the build elsewhere.

The rest of the colleague's tree (their own VAM firmware, PKI tooling,
station-link Python tools, the V2X2MAP bridge) stays out of this repository
and gitignored; nothing is pushed to their repository. NOTES.md, docs/06,
TODO.md and the pcap verifier's usage line point at the new location.

obu-firmware/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;
+}